feat(cutover): hard legacy cutover — drop projects/stacks/sites/deploys

The clean-break delete that closes the workload-first refactor arc.
Net diff: ~30 backend files deleted, ~20 modified, ~12k LOC removed
on the Go side; entire /projects /stacks /sites /deploy frontend
trees gone; ~6.7k LOC removed on the Svelte/TypeScript side.

Backend
- API handlers gone: internal/api/{projects,stages,stage_env,stacks,
  static_sites,deploys,instances,volume_browser}.go
- Store CRUD + tests gone: internal/store/{projects,stages,stage_env,
  stacks,static_sites,static_site_secrets,deploys,poll_state,volumes,
  workload_sync}.go (+ _test.go siblings)
- Legacy deployer pipeline gone: internal/deployer/{bluegreen,promote,
  rollback,subdomain,resolver_test}.go; deployer.go trimmed to just the
  dispatch surface used by the plugin pipeline
- internal/staticsite/{manager,healthcheck}.go and
  internal/stack/manager.go gone (the rest of those packages stay as
  helpers imported by the static + compose plugins)
- internal/registry/poller.go gone (legacy registry poller)
- internal/volume.ResolvePath gone; ResolveWorkloadPath stays
- internal/webhook: handleWebhook (project) + handleSiteWebhook (site)
  gone; only POST /api/webhook/triggers/{secret} remains
- workload-side webhook URL handlers (getWorkloadWebhook +
  regenerateWorkloadWebhook + EnsureWorkloadWebhookSecret +
  SetWorkloadWebhookSecret + GetWorkloadByWebhookSecret) gone — they
  minted URLs that would 404 against the new trigger-only ingress
- cmd/server/main.go: dropped staticsite.Manager, stack.Manager,
  staticsite.HealthChecker, registry poller, SetSiteSyncTriggerer,
  SetStaticSiteManager, SetStackManager, wireStaticBackend
- store/store.go: idempotent DROP TABLE IF EXISTS for every legacy
  table (projects, stages, stage_env, volumes, deploys, deploy_logs,
  poll_states, stacks, stack_revisions, stack_deploys, static_sites,
  static_site_secrets); FK order children-then-parents
- store/models.go: dropped Project, Stage, Deploy, DeployLog, StageEnv,
  Volume, StaticSite, StaticSiteSecret, Stack, StackRevision,
  StackDeploy types; kept WorkloadKind constants as documented strings
- internal/store/helpers.go (new): BoolToInt, rowScanner,
  GenerateWebhookSecret extracted from deleted CRUD files
- internal/api/secrets.go (new): forwards to store.GenerateWebhookSecret
  so api + store paths share one secret-generation impl (no
  panic-vs-UUID-fallback divergence)
- internal/reconciler/reconciler.go: dropped legacy stack-by-compose
  + static-site label paths; only canonical tinyforge.workload.id
  dispatch remains
- providers (gitea_content/github_provider/gitlab_provider) gained
  path-traversal rejection on every tree entry
- internal/webhook ParsedImage / ParseImageRef demoted to package-
  private (no external callers)

Frontend
- /projects /stacks /sites /deploy routes deleted (entire trees)
- ProjectCard / InstanceCard / StaleContainerCard components deleted
- api.ts: dropped every project/stage/stack/site/deploy/instance
  helper + types (Project, Stage, Stack, StaticSite, Deploy,
  Instance, Volume, etc.); kept Workload, Container, App, Settings,
  Registry, EventTrigger, LogScanRule, webhook envelopes
- WorkloadWebhook type + getWorkloadWebhook/regenerateWorkloadWebhook
  api functions gone (mirror of the backend deletion above)
- web/src/routes/+layout.svelte: dropped /projects /sites /stacks
  /deploy nav entries, trimmed quick-nav keymap
- web/src/routes/+page.svelte: dashboard rewrite — reads
  listWorkloads + listContainers only; 4-card stat grid
  (workloads/running/failed/stale) + recent workloads strip
- navCounts.ts, SystemHealthCard.svelte, ContainerLogs.svelte,
  ContainerStats.svelte, StatusBadge.svelte, TagCombobox.svelte,
  proxies/+page.svelte, containers/+page.svelte all rewired to the
  workload-first surface
- AbortController plumbing on dashboard, nav-counts, stale page,
  SystemHealthCard so navigation doesn't leave dangling fetches
- i18n: dropped projects.*, projectDetail.*, envEditor.*,
  volumeEditor.*, volumeBrowser.*, quickDeploy.*, sites.*, stacks.*,
  instance.*, confirm.* namespaces; en/ru parity preserved (1042
  keys each)

Hardening from go-reviewer + security-reviewer + typescript-reviewer
subagent passes (0 CRITICAL across all three; 1 HIGH + ~12 MEDIUM
addressed inline before commit):

- Sec H1: dead-end workload webhook URL handlers (would mint URLs
  that 404 the new trigger-only ingress) deleted across backend +
  frontend
- Go M1: IsTerminalDeployStatus dropped (no production callers)
- Go M2: ParsedImage/ParseImageRef lowercased (in-package only)
- Go M6: generateWebhookSecret unified — api shim forwards to
  store.GenerateWebhookSecret
- Doc/comment freshness: stage_id (no longer FK), ProxyRoute legacy
  field names, workloadIDRow rationale, webhook_deliveries.target_type
  enum, WebhookDeliveryLog component header

Doc
- WORKLOAD_REFACTOR_TODO: cutover marked DONE; all three Priority 1
  items are now shipped. Next focus is Priority 3 polish (apps.* i18n
  + codemap entries) and Priority 4 tests.

Behavioral notes for operators upgrading from a pre-cutover build
- Existing rows in the dropped tables disappear on first boot.
- Legacy webhook URLs at /api/webhook/{secret} and
  /api/webhook/sites/{secret} return 404; CI configs must repoint to
  /api/webhook/triggers/{secret} (the trigger-split boot backfill
  lifted any embedded workload secret onto a Trigger row, so the
  secret value itself carries over).
- Frontend routes /projects /stacks /sites /deploy are gone; nav
  links replaced with /apps and /triggers.

internal/store/workloads.go

@@ -93,24 +93,6 @@ func (s *Store) GetWorkloadByRef(kind WorkloadKind, refID string) (Workload, err
 	return w, nil
 }
 
-// GetWorkloadByWebhookSecret looks up a workload by its inbound webhook URL secret.
-// Returns ErrNotFound when no match — used by the webhook router.
-func (s *Store) GetWorkloadByWebhookSecret(secret string) (Workload, error) {
-	if secret == "" {
-		return Workload{}, fmt.Errorf("empty secret: %w", ErrNotFound)
-	}
-	w, err := scanWorkload(s.db.QueryRow(
-		`SELECT `+workloadColumns+` FROM workloads WHERE webhook_secret = ?`, secret,
-	))
-	if errors.Is(err, sql.ErrNoRows) {
-		return Workload{}, ErrNotFound
-	}
-	if err != nil {
-		return Workload{}, fmt.Errorf("query workload by webhook secret: %w", err)
-	}
-	return w, nil
-}
-
 // ListWorkloads returns all workloads, optionally filtered by kind. Pass
 // empty string to get every workload regardless of kind.
 func (s *Store) ListWorkloads(kind WorkloadKind) ([]Workload, error) {
@@ -231,40 +213,12 @@ func (s *Store) ListChildrenByParent(parentID string) ([]Workload, error) {
 	return out, rows.Err()
 }
 
-// SetWorkloadWebhookSecret rotates the inbound webhook URL secret. Pass
-// empty to disable inbound webhooks for this workload.
-func (s *Store) SetWorkloadWebhookSecret(id, secret string) error {
-	result, err := s.db.Exec(
-		`UPDATE workloads SET webhook_secret=?, updated_at=? WHERE id=?`,
-		secret, Now(), id,
-	)
-	if err != nil {
-		return fmt.Errorf("update workload webhook_secret: %w", err)
-	}
-	n, _ := result.RowsAffected()
-	if n == 0 {
-		return fmt.Errorf("workload %s: %w", id, ErrNotFound)
-	}
-	return nil
-}
-
-// EnsureWorkloadWebhookSecret returns the current secret, generating one
-// lazily for workloads that predate the column. Mirrors the project /
-// site equivalents.
-func (s *Store) EnsureWorkloadWebhookSecret(id string) (string, error) {
-	w, err := s.GetWorkloadByID(id)
-	if err != nil {
-		return "", err
-	}
-	if w.WebhookSecret != "" {
-		return w.WebhookSecret, nil
-	}
-	secret := generateWebhookSecret()
-	if err := s.SetWorkloadWebhookSecret(id, secret); err != nil {
-		return "", err
-	}
-	return secret, nil
-}
+// Workload-level webhook secret accessors (Get/Set/Ensure) were dropped
+// in the hard legacy cutover: the inbound `/api/webhook/workloads/...`
+// route is gone. The trigger-split refactor's boot backfill still reads
+// the `workloads.webhook_secret` column directly via SQL to lift any
+// pre-cutover embedded secret onto its standalone Trigger row, then the
+// column is effectively dead.
 
 // DeleteWorkloadByRef removes the workload paired with a given (kind, ref_id).
 // Idempotent — returns nil if no row exists, since the kind-specific Delete