feat(uploads): direct-to-B2 presigned uploads with content-length-range policy

Replaces the multipart-via-API path for image uploads with a three-step
direct-to-storage flow:

  1. Client POSTs /api/uploads/presign with content_length + content_type;
     server validates size (10 MB cap), mime allow-list per category, rate
     limit (50/hour/user via Redis sliding window), and concurrent unclaimed
     cap (10 in-flight per user). On success it persists a pending_uploads
     row, signs an S3 POST policy with content-length-range bound to the
     claimed length ±256 bytes, and returns the URL+fields.
  2. Client POSTs the bytes directly to B2 using the signed policy. B2
     enforces size, content-type, and key match before accepting.
  3. Client passes upload_ids[] to /api/task-completions/ or /api/documents/.
     Service HEADs each B2 object, verifies size matches expected_bytes
     within slack, marks pending_uploads claimed_at, and creates the
     associated TaskCompletionImage / DocumentImage rows.

Bytes never traverse our API server. The 1 MB Echo BodyLimit middleware
that was rejecting all task-completion image uploads becomes irrelevant
for this path. Existing multipart endpoints stay functional alongside,
soak-testing the new path before legacy removal.

Cleanup:
  - cmd/worker registers a new hourly cron (TypeUploadCleanup, "30 * * * *")
    that reaps pending_uploads where claimed_at IS NULL AND expires_at < NOW().
    Reaps both the B2 object and the row.
  - B2 bucket lifecycle rule on `uploads/` prefix (7 days hide → 1 day delete)
    documented in deploy-k3s/manifests/b2-lifecycle.md as a backstop.

Schema:
  - migrations/000002_pending_uploads.sql adds the table + partial index for
    cleanup + nullable pending_upload_id FKs on task_taskcompletionimage and
    task_documentimage.

Policy (single tier, no free/pro split):
  - 10 MB cap per upload
  - 50 presigns/hour/user
  - 10 concurrent unclaimed uploads/user
  - allow-list: jpeg/png/heic/heif/webp for image categories;
    + pdf for document_file

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/router/router.go

@@ -260,6 +260,20 @@ func SetupRouter(deps *Dependencies) *echo.Echo {
 	if deps.StorageService != nil {
 		uploadHandler = handlers.NewUploadHandler(deps.StorageService, services.NewFileOwnershipService(deps.DB))
 		mediaHandler = handlers.NewMediaHandler(documentRepo, taskRepo, residenceRepo, deps.StorageService)
+
+		// Presigned-URL upload path requires S3-compatible backend. With local
+		// disk we silently skip; the route returns 500 if hit.
+		if s3 := deps.StorageService.S3Backend(); s3 != nil {
+			pendingUploadRepo := repositories.NewPendingUploadRepository(deps.DB)
+			uploadService := services.NewUploadService(pendingUploadRepo, s3, &cfg.Storage, deps.Cache)
+			uploadHandler.SetUploadService(uploadService)
+			// Task and document services need the upload service to claim
+			// pending_uploads rows when /api/task-completions/ or /api/documents/
+			// is called with `upload_ids: [..]` instead of multipart.
+			taskService.SetUploadService(uploadService)
+			documentService.SetStorageService(deps.StorageService)
+			documentService.SetUploadService(uploadService)
+		}
 	}
 
 	// Legacy Prometheus-shaped metrics from internal/monitoring (consumed by
@@ -724,6 +738,7 @@ func setupUploadRoutes(api *echo.Group, uploadHandler *handlers.UploadHandler) {
 		uploads.POST("/image/", uploadHandler.UploadImage)
 		uploads.POST("/document/", uploadHandler.UploadDocument)
 		uploads.POST("/completion/", uploadHandler.UploadCompletion)
+		uploads.POST("/presign/", uploadHandler.PresignUpload)
 		uploads.DELETE("/", uploadHandler.DeleteFile)
 	}
 }