feat(webhook): inbound delivery audit log

Persists every inbound webhook hit (project + site) so users can debug
"why didn't my deploy fire?" without grepping daemon logs. Surfaces a
14-day rolling history under the WebhookPanel on each project + site
detail page; refreshes every 30s while open. Daily cron prunes records
older than 14 days alongside the existing event log prune.

Schema:
- webhook_deliveries(id, target_type, target_id, target_name, received_at,
  source_ip, signature_state, status_code, outcome, detail, body_size)
- indexes on (target_type,target_id,received_at) and (received_at)

Backend:
- store: WebhookDelivery model + Insert/List/Prune helpers
- webhook/handler: deferred recordDelivery() captures the final outcome
  on every return path including HMAC rejects, image mismatch, no-stage,
  auto_deploy=false, and successful deploys; signatureStateFor()
  classifies "unconfigured" vs "missing" vs "invalid" vs "valid"
- api: GET /api/{projects,sites}/{id}/webhook/deliveries with
  parseLimit() helper (default 50, max 200)
- main: daily prune cron retains the last 14 days

Frontend:
- WebhookDeliveryLog.svelte: panel with refresh button, status code +
  outcome + signature badges, relative time tooltip-on-hover for
  absolute time, source IP column
- Mounted below WebhookPanel on project + site detail pages
- en/ru i18n strings for outcome/signature enums and column labels

internal/api/router.go

@@ -249,6 +249,7 @@ func (s *Server) Router() chi.Router {
 					r.Post("/webhook/signing-secret/regenerate", s.regenerateProjectSigningSecret)
 					r.Delete("/webhook/signing-secret", s.disableProjectSigningSecret)
 					r.Put("/webhook/require-signature", s.updateProjectSigningRequirement)
+					r.Get("/webhook/deliveries", s.listProjectWebhookDeliveries)
 
 					// Per-project outgoing-webhook signing & test.
 					r.Get("/notification-secret", s.getProjectNotificationSecret)
@@ -332,6 +333,7 @@ func (s *Server) Router() chi.Router {
 					r.Post("/webhook/signing-secret/regenerate", s.regenerateStaticSiteSigningSecret)
 					r.Delete("/webhook/signing-secret", s.disableStaticSiteSigningSecret)
 					r.Put("/webhook/require-signature", s.updateStaticSiteSigningRequirement)
+					r.Get("/webhook/deliveries", s.listStaticSiteWebhookDeliveries)
 
 					// Per-site outgoing-webhook signing & test.
 					r.Get("/notification-secret", s.getStaticSiteNotificationSecret)