T-130: MCP server over HTTP+SSE for /ide integration

Seventh slice of T-99. clide now advertises itself to Claude Code's
/ide command and serves a working MCP endpoint over HTTP+SSE per
D-73 (the Q-33 transport decision, locked in this commit).

What lands:
* D-73 — MCP transport for /ide is SSE over HTTP. Resolves Q-33;
  references D-68 + D-72.
* lib/src/ipc/mcp_server.dart — McpServer class. localhost HTTP
  listener on a random port; GET /sse opens a long-lived SSE stream
  with an initial endpoint event carrying the session id; POST
  /messages?sessionId=... accepts JSON-RPC requests and replies via
  the matching SSE stream. JSON-RPC handlers for initialize,
  tools/list, tools/call.
* Discovery file at $HOME/.claude/ide/<pid>.lock with the workspace
  + url so `/ide` can find us. Removed on stop.
* The two /ide minimum tools (mcp__ide__getDiagnostics,
  mcp__ide__executeCode) ship as stubs — real implementations need
  the analyzer integration / a clide eval surface, both follow-ups.
* main.dart starts the MCP server alongside the unix IPC server on
  daemonClientFactory and project switch. Failure non-fatal — the
  UI runs without MCP.
* 12 server tests cover lifecycle (start/stop, lock file), unknown
  paths, full JSON-RPC round-trip for all four methods, error
  responses, and edge cases (unknown session, malformed JSON,
  notification without id).

The "Claude Code's /ide discovers and connects" smoke is deferred to
T-131 wrap-up since it needs a real Claude Code session against the
running app — out of scope for unit/widget tests.

Co-Authored-By: Claude <noreply@anthropic.com>

lib/main.dart

@@ -39,6 +39,7 @@ import 'package:clide/src/editor/registry.dart' show EditorRegistry;
 import 'package:clide/src/git/client.dart';
 import 'package:clide/src/cli/argv_dispatch.dart';
 import 'package:clide/src/ipc/envelope.dart';
+import 'package:clide/src/ipc/mcp_server.dart';
 import 'package:clide/src/ipc/paths.dart' show workspaceSocketPath;
 import 'package:clide/src/ipc/server.dart';
 import 'package:clide/src/panes/event_sink.dart';
@@ -86,6 +87,11 @@ Future<void> main() async {
   // back to it over the socket so all IPC — including from UI widgets
   // in the same process — goes through the wire contract (T-127).
   IpcServer? ipcServer;
+  // MCP server (T-130, per D-68 + D-73). Localhost HTTP+SSE, advertised
+  // via $HOME/.claude/ide/<pid>.lock so Claude Code's /ide command
+  // discovers it. Restarted alongside the unix server on project
+  // switch so the discovery file reports the current workspace.
+  McpServer? mcpServer;
   final ipcLog = Logger();
 
   Future<void> swapIpcServer(DaemonDispatcher dispatcher, Directory workRoot) async {
@@ -96,6 +102,11 @@ Future<void> main() async {
       ipcLog.warn('ipc', 'stop failed during swap: $e');
       ipcLog.debug('ipc', '$st');
     }
+    try {
+      await mcpServer?.stop();
+    } catch (e) {
+      ipcLog.warn('mcp', 'stop failed during swap: $e');
+    }
     final server = IpcServer(
       dispatcher: dispatcher,
       workspaceRoot: workRoot.path,
@@ -109,6 +120,14 @@ Future<void> main() async {
       ipcLog.error('ipc', 'server start failed', error: e, stackTrace: st);
       return;
     }
+    final mcp = McpServer(workspaceRoot: workRoot.path, log: ipcLog);
+    mcpServer = mcp;
+    try {
+      await mcp.start();
+    } catch (e, st) {
+      ipcLog.warn('mcp', 'MCP server start failed (non-fatal): $e');
+      ipcLog.debug('mcp', '$st');
+    }
     // Point the in-process DaemonClient at the new socket. On first
     // boot (no client yet) the daemonClientFactory below kicks it
     // off; on project switch we just reconnect to the new path.