Steps 12 & 12b: gRPC server and directory recursion + mirror.

Step 12: GardenSync gRPC server with 5 RPC handlers — PushManifest
(timestamp comparison, missing blob detection), PushBlobs (chunked
streaming, manifest replacement), PullManifest, PullBlobs, Prune.
Added store.List() and garden.ListBlobs()/DeleteBlob() for prune.
In-process tests via bufconn.

Step 12b: Add now recurses directories (walks files/symlinks, skips
dir entries). Mirror up syncs filesystem → manifest (add new, remove
deleted, rehash changed). Mirror down syncs manifest → filesystem
(restore + delete untracked with optional confirm). 7 tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

garden/garden.go

@@ -127,6 +127,16 @@ func (g *Garden) ReplaceManifest(m *manifest.Manifest) error {
 	return nil
 }
 
+// ListBlobs returns all blob hashes in the store.
+func (g *Garden) ListBlobs() ([]string, error) {
+	return g.store.List()
+}
+
+// DeleteBlob removes a blob from the store by hash.
+func (g *Garden) DeleteBlob(hash string) error {
+	return g.store.Delete(hash)
+}
+
 // addEntry adds a single file or symlink to the manifest. The abs path must
 // already be resolved and info must come from os.Lstat. If skipDup is true,
 // already-tracked paths are silently skipped instead of returning an error.