feat(upload): add programmatic Ingest service and file-upload skill

Introduce upload/ingest as the single domain entry for storing files,
writing w_uploads records, and maintaining incremental stats. Refactor
HTTP UploadFile and delete handlers to delegate to ingest, fix stats
decrement ordering on Remove, and document usage in the file-upload skill.

internal/apps/upload/exports.go

@@ -7,6 +7,7 @@ import (
 	"github.com/Rain-kl/Wavelet/internal/apps/upload/cache"
 	"github.com/Rain-kl/Wavelet/internal/apps/upload/filesrv"
 	"github.com/Rain-kl/Wavelet/internal/apps/upload/handler"
+	"github.com/Rain-kl/Wavelet/internal/apps/upload/ingest"
 	uploadstats "github.com/Rain-kl/Wavelet/internal/apps/upload/stats"
 	uploadtask "github.com/Rain-kl/Wavelet/internal/apps/upload/task"
 	"github.com/Rain-kl/Wavelet/internal/apps/upload/util"
@@ -28,6 +29,36 @@ var (
 	ServeFileByID          = filesrv.ServeFileByID
 )
 
+// Programmatic ingest API
+var (
+	Ingest      = ingest.Ingest
+	Remove      = ingest.Remove
+	RemoveOwned = ingest.RemoveOwned
+	FindByHash  = ingest.FindByHash
+)
+
+// Ingest policy constants
+const (
+	PolicyCreate            = ingest.PolicyCreate
+	PolicyDedupNewRecord    = ingest.PolicyDedupNewRecord
+	PolicyResolveExisting   = ingest.PolicyResolveExisting
+)
+
+type (
+	// IngestRequest is the programmatic upload ingest payload.
+	IngestRequest = ingest.Request
+	// IngestResult reports ingest side effects.
+	IngestResult = ingest.Result
+	// IngestPolicy controls hash-collision behavior during ingest.
+	IngestPolicy = ingest.Policy
+)
+
+// Ingest errors
+var (
+	ErrIngestForbidden      = ingest.ErrForbidden
+	ErrIngestStorageReadOnly = ingest.ErrStorageReadOnly
+)
+
 // Cache management
 var (
 	ResetAccessCaches              = cache.ResetAccessCaches
@@ -36,7 +67,9 @@ var (
 
 // Stats
 var (
-	ApplyUploadStatsAdd    = uploadstats.ApplyUploadStatsAdd
+	// Deprecated: use upload.Ingest or upload.Remove; stats are applied internally.
+	ApplyUploadStatsAdd = uploadstats.ApplyUploadStatsAdd
+	// Deprecated: use upload.Ingest or upload.Remove; stats are applied internally.
 	ApplyUploadStatsRemove = uploadstats.ApplyUploadStatsRemove
 	RebuildUploadStats     = uploadstats.RebuildUploadStats
 )