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)

cmd/memoh/serve.go

@@ -220,9 +220,9 @@ func provideAgentRuntimeManager(log *slog.Logger, cfg config.Config) *agentrunti
 func provideMemoryLLM(modelsService *models.Service, queries *dbsqlc.Queries, log *slog.Logger) memprovider.LLM {
 	return &lazyLLMClient{modelsService: modelsService, queries: queries, timeout: 30 * time.Second, logger: log}
 }
-func provideMemoryProviderRegistry(log *slog.Logger, chatService *conversation.Service, accountService *accounts.Service, containerdHandler *handlers.ContainerdHandler) *memprovider.Registry {
+func provideMemoryProviderRegistry(log *slog.Logger, chatService *conversation.Service, accountService *accounts.Service, manager *mcp.Manager) *memprovider.Registry {
 	registry := memprovider.NewRegistry(log)
-	builtinRuntime := handlers.NewBuiltinMemoryRuntime(containerdHandler.FSService())
+	builtinRuntime := handlers.NewBuiltinMemoryRuntime(manager)
 	registry.RegisterFactory(memprovider.BuiltinType, func(id string, config map[string]any) (memprovider.Provider, error) {
 		return memprovider.NewBuiltinProvider(log, builtinRuntime, chatService, accountService), nil
 	})
@@ -335,7 +335,7 @@ func provideMemoryHandler(log *slog.Logger, botService *bots.Service, accountSer
 	h := handlers.NewMemoryHandler(log, botService, accountService)
 	h.SetMemoryRegistry(memoryRegistry)
 	h.SetSettingsService(settingsService)
-	h.SetFSService(containerdHandler.FSService())
+	h.SetMCPClientProvider(manager)
 	return h
 }
 func provideAuthHandler(log *slog.Logger, accountService *accounts.Service, rc *boot.RuntimeConfig) *handlers.AuthHandler {
@@ -356,16 +356,9 @@ func (h *memohAuthHandler) Register(e *echo.Echo) {
 	e.POST("/api/auth/login", h.inner.Login)
 	e.POST("/api/auth/refresh", h.inner.Refresh)
 }
-func provideMediaService(log *slog.Logger, cfg config.Config) (*media.Service, error) {
-	dataRoot := strings.TrimSpace(cfg.MCP.DataRoot)
-	if dataRoot == "" {
-		dataRoot = config.DefaultDataRoot
-	}
-	provider, err := containerfs.New(dataRoot)
-	if err != nil {
-		return nil, fmt.Errorf("init media provider: %w", err)
-	}
-	return media.NewService(log, provider), nil
+func provideMediaService(log *slog.Logger, manager *mcp.Manager) *media.Service {
+	provider := containerfs.New(manager)
+	return media.NewService(log, provider)
 }
 func provideUsersHandler(log *slog.Logger, accountService *accounts.Service, identityService *identities.Service, botService *bots.Service, routeService *route.DBService, channelStore *channel.Store, channelLifecycle *channel.Lifecycle, channelManager *channel.Manager, registry *channel.Registry) *handlers.UsersHandler {
 	return handlers.NewUsersHandler(log, accountService, identityService, botService, routeService, channelStore, channelLifecycle, channelManager, registry)
@@ -506,7 +499,7 @@ func startAgentRuntime(lc fx.Lifecycle, manager *agentruntime.Manager) {
 		OnStop:  func(ctx context.Context) error { return manager.Stop(ctx) },
 	})
 }
-func startServer(lc fx.Lifecycle, logger *slog.Logger, srv *memohServer, shutdowner fx.Shutdowner, cfg config.Config, queries *dbsqlc.Queries, botService *bots.Service, containerdHandler *handlers.ContainerdHandler, mcpConnService *mcp.ConnectionService, toolGateway *mcp.ToolGatewayService, channelManager *channel.Manager) {
+func startServer(lc fx.Lifecycle, logger *slog.Logger, srv *memohServer, shutdowner fx.Shutdowner, cfg config.Config, queries *dbsqlc.Queries, botService *bots.Service, containerdHandler *handlers.ContainerdHandler, manager *mcp.Manager, mcpConnService *mcp.ConnectionService, toolGateway *mcp.ToolGatewayService, channelManager *channel.Manager) {
 	fmt.Printf("Starting Memoh Agent %s\n", version.GetInfo())
 	lc.Append(fx.Hook{
 		OnStart: func(ctx context.Context) error {
@@ -514,6 +507,10 @@ func startServer(lc fx.Lifecycle, logger *slog.Logger, srv *memohServer, shutdow
 				return err
 			}
 			botService.SetContainerLifecycle(containerdHandler)
+			botService.SetContainerReachability(func(ctx context.Context, botID string) error {
+				_, err := manager.MCPClient(ctx, botID)
+				return err
+			})
 			botService.AddRuntimeChecker(healthcheck.NewRuntimeCheckerAdapter(mcpchecker.NewChecker(logger, mcpConnService, toolGateway)))
 			botService.AddRuntimeChecker(healthcheck.NewRuntimeCheckerAdapter(channelchecker.NewChecker(logger, channelManager)))
 			go func() {