feat(mcp): replace bind-mount+exec with in-container gRPC service (#179)

Replace the host bind-mount + containerd exec approach with a per-bot
in-container gRPC server (ContainerService, port 9090). All file I/O,
exec, and MCP stdio sessions now go through gRPC instead of running
shell commands or reading host-mounted directories.

Architecture changes:
- cmd/mcp: rewritten as a gRPC server (ContainerService) with full
  file and exec API (ReadFile, WriteFile, ListDir, ReadRaw, WriteRaw,
  Exec, Stat, Mkdir, Rename, DeleteFile)
- internal/mcp/mcpcontainer: protobuf definitions and generated stubs
- internal/mcp/mcpclient: gRPC client wrapper with connection pool
  (Pool) and Provider interface for dependency injection
- mcp.Manager: add per-bot IP cache, gRPC connection pool, and
  SetContainerIP/MCPClient methods; remove DataDir/Exec helpers
- containerd.Service: remove ExecTask/ExecTaskStreaming; network setup
  now returns NetworkResult{IP} for pool routing
- internal/fs/service.go: deleted (replaced by mcpclient)
- handlers/fs.go: deleted; MCP stdio session logic moved to mcp_stdio.go
- container provider Executor: all tools (read/write/list/edit/exec)
  now call gRPC client instead of running shell via exec
- storefs, containerfs, media, skills, memory: all I/O ported to
  mcpclient.Provider

Database:
- migration 0022: drop host_path column from containers table

One-time data migration:
- migrateBindMountData: on first Start() after upgrade, copies old
  bind-mount data into the container via gRPC, then renames src dir
  to prevent re-migration; runs in background goroutine

Bug fixes:
- mcp_stdio: callRaw now returns full JSON-RPC envelope
  {"jsonrpc","id","result"|"error"} matching protocol spec;
  explicit "initialize" call now advances session init state to
  prevent duplicate handshake on next non-initialize call
- mcpclient Pool: properly evict stale gRPC connection after snapshot
  replace (container process recreated); use SetContainerIP instead
  of direct map write so IP changes always evict pool entry
- migrateBindMountData: walkErr on directories now counted as failure
  so partially-walked trees don't get incorrectly marked as migrated
- cmd/mcp/Dockerfile: removed dead file (docker/Dockerfile.mcp is the
  canonical production build)

Tests:
- provider_test.go: restored with bufconn in-process gRPC mock
  (fakeContainerService + staticProvider), 14 cases covering all 5
  tools plus edge cases
- mcp_session_test.go: new, covers JSON-RPC envelope, init state
  machine, pending cleanup on cancel/close, readLoop cancel
- storefs/service_test.go: restored (pure function roundtrip tests)

internal/db/sqlc/containers.sql.go

@@ -21,7 +21,7 @@ func (q *Queries) DeleteContainerByBotID(ctx context.Context, botID pgtype.UUID)
 }
 
 const getContainerByBotID = `-- name: GetContainerByBotID :one
-SELECT id, bot_id, container_id, container_name, image, status, namespace, auto_start, host_path, container_path, created_at, updated_at, last_started_at, last_stopped_at FROM containers WHERE bot_id = $1 ORDER BY updated_at DESC LIMIT 1
+SELECT id, bot_id, container_id, container_name, image, status, namespace, auto_start, container_path, created_at, updated_at, last_started_at, last_stopped_at FROM containers WHERE bot_id = $1 ORDER BY updated_at DESC LIMIT 1
 `
 
 func (q *Queries) GetContainerByBotID(ctx context.Context, botID pgtype.UUID) (Container, error) {
@@ -36,7 +36,6 @@ func (q *Queries) GetContainerByBotID(ctx context.Context, botID pgtype.UUID) (C
 		&i.Status,
 		&i.Namespace,
 		&i.AutoStart,
-		&i.HostPath,
 		&i.ContainerPath,
 		&i.CreatedAt,
 		&i.UpdatedAt,
@@ -47,7 +46,7 @@ func (q *Queries) GetContainerByBotID(ctx context.Context, botID pgtype.UUID) (C
 }
 
 const listAutoStartContainers = `-- name: ListAutoStartContainers :many
-SELECT id, bot_id, container_id, container_name, image, status, namespace, auto_start, host_path, container_path, created_at, updated_at, last_started_at, last_stopped_at FROM containers WHERE auto_start = true ORDER BY updated_at DESC
+SELECT id, bot_id, container_id, container_name, image, status, namespace, auto_start, container_path, created_at, updated_at, last_started_at, last_stopped_at FROM containers WHERE auto_start = true ORDER BY updated_at DESC
 `
 
 func (q *Queries) ListAutoStartContainers(ctx context.Context) ([]Container, error) {
@@ -68,7 +67,6 @@ func (q *Queries) ListAutoStartContainers(ctx context.Context) ([]Container, err
 			&i.Status,
 			&i.Namespace,
 			&i.AutoStart,
-			&i.HostPath,
 			&i.ContainerPath,
 			&i.CreatedAt,
 			&i.UpdatedAt,
@@ -126,7 +124,7 @@ func (q *Queries) UpdateContainerStopped(ctx context.Context, botID pgtype.UUID)
 const upsertContainer = `-- name: UpsertContainer :exec
 INSERT INTO containers (
   bot_id, container_id, container_name, image, status, namespace, auto_start,
-  host_path, container_path, last_started_at, last_stopped_at
+  container_path, last_started_at, last_stopped_at
 )
 VALUES (
   $1,
@@ -138,8 +136,7 @@ VALUES (
   $7,
   $8,
   $9,
-  $10,
-  $11
+  $10
 )
 ON CONFLICT (container_id) DO UPDATE SET
   bot_id = EXCLUDED.bot_id,
@@ -148,7 +145,6 @@ ON CONFLICT (container_id) DO UPDATE SET
   status = EXCLUDED.status,
   namespace = EXCLUDED.namespace,
   auto_start = EXCLUDED.auto_start,
-  host_path = EXCLUDED.host_path,
   container_path = EXCLUDED.container_path,
   last_started_at = EXCLUDED.last_started_at,
   last_stopped_at = EXCLUDED.last_stopped_at,
@@ -163,7 +159,6 @@ type UpsertContainerParams struct {
 	Status        string             `json:"status"`
 	Namespace     string             `json:"namespace"`
 	AutoStart     bool               `json:"auto_start"`
-	HostPath      pgtype.Text        `json:"host_path"`
 	ContainerPath string             `json:"container_path"`
 	LastStartedAt pgtype.Timestamptz `json:"last_started_at"`
 	LastStoppedAt pgtype.Timestamptz `json:"last_stopped_at"`
@@ -178,7 +173,6 @@ func (q *Queries) UpsertContainer(ctx context.Context, arg UpsertContainerParams
 		arg.Status,
 		arg.Namespace,
 		arg.AutoStart,
-		arg.HostPath,
 		arg.ContainerPath,
 		arg.LastStartedAt,
 		arg.LastStoppedAt,