chore(workload): close the workload-first arc — apps i18n + codemap + tests

Closes the workload-first refactor by landing the Priority 3 polish
items and the Priority 4 test gap. Net: ~2,400 lines added,
~350 lines modified across 13 files.

Priority 3 — polish
- apps.* i18n namespace: 276 new keys across apps.list.* (27),
  apps.new.* (91, sibling of existing apps.new.triggers.*), and
  apps.detail.* (158, sibling of existing apps.detail.bindings.*).
  EN+RU at 1314 keys each, perfectly in sync. /apps, /apps/new,
  /apps/[id] now render entirely from i18n.
- New codemap docs/CODEMAPS/workload-plugin.md (238 lines):
  Source × Trigger contract, dispatch seam, webhook fan-out path,
  recipes for adding a new Source or Trigger kind. Plus
  docs/CODEMAPS/INDEX.md gateway.

Priority 4 — tests
- internal/api/workloads_test.go (new, ~30 subtests): /api/workloads
  CRUD + deploy + delete + env + volumes + chain + promote-from +
  triggers list/inline-bind + auth gating + standalone /api/triggers
  CRUD (create / dup-409 / kind filter / delete). Uses real
  POST handlers via httptest.NewServer + a fake plugin source
  registered under "testfakesource".
- internal/deployer/dispatch_test.go (new, 11 tests):
  DispatchPlugin / DispatchTeardown / DispatchReconcile happy +
  unknown-kind + propagated-error each; PluginDeps wiring; a real
  2s-bounded RWMutex deadlock probe on PluginDeps vs SetDNSProvider.
- internal/workload/plugin/source/compose/compose_test.go (new,
  ~26 subtests): composeProjectName sanitization,
  writeYAML / writeYAMLIfChanged hash short-circuit, Validate happy
  + bad inputs, Kind / SchemaSample.

Coverage delta on the workload-plugin path:
- internal/api: 1.1% → 16.0%
- internal/deployer: 0% → 54.1%
- internal/workload/plugin/source/compose: 0% → 38.5%
- Trigger plugins already at 87-95% from the trigger-split work.

Production fix surfaced by the tests
- store.CreateWorkload now self-references RefID = ID when caller
  leaves RefID empty (the typical plugin-native path). The api
  layer's broken backfill loop (called UpdateWorkload, which
  deliberately omits ref_id) is gone. Multiple sibling plugin
  workloads can now coexist under the UNIQUE(kind, ref_id) constraint.

Review fixes addressed before commit
- CRITICAL: deadlock-detect test gained a real 2s time.After (was
  selecting on context.Background().Done() which never fires).
- HIGH: happy-path test now hard-asserts RefID = ID (was a t.Logf
  that would silently pass after a production fix).
- HIGH: standalone /api/triggers CRUD coverage added (was bypassed
  by the workload-side bind flow).
- HIGH: seedWorkload bypass deleted; tests now go through the
  real POST /api/workloads handler.
- MEDIUM: withTempDir restore is a no-op (t.Setenv auto-restores);
  dead `old := os.Getenv(...)` capture removed.
- MEDIUM: list-workloads test now asserts ID membership, not just
  count.

Doc
- WORKLOAD_REFACTOR_TODO: all three Priority 1 items, Priority 3
  polish, and Priority 4 tests marked DONE. The workload-first arc
  is closed.

internal/store/workloads.go

@@ -28,12 +28,19 @@ func scanWorkload(scanner interface{ Scan(...any) error }) (Workload, error) {
 	return w, err
 }
 
-// CreateWorkload inserts a new workload row. The (Kind, RefID) pair must be
-// unique; the caller is responsible for matching this to a project/stack/site.
+// CreateWorkload inserts a new workload row. The (Kind, RefID) pair
+// must be unique; for plugin-native rows (Kind="plugin") the caller
+// typically leaves RefID empty and we self-reference it to the row's
+// own ID so the UNIQUE(kind, ref_id) constraint holds for many sibling
+// plugin workloads. Legacy bridge code that wired ref_id to a
+// project/stack/site row was deleted in the hard cutover.
 func (s *Store) CreateWorkload(w Workload) (Workload, error) {
 	if w.ID == "" {
 		w.ID = uuid.New().String()
 	}
+	if w.RefID == "" {
+		w.RefID = w.ID
+	}
 	w.CreatedAt = Now()
 	w.UpdatedAt = w.CreatedAt