feat: replace SpawnDetector with MCP server for spawn1337 protocol

Instead of parsing terminal output for <spawn1337> tags, spawn capabilities
are now exposed as native MCP tools that Claude Code can call directly.
The MCP server (stdio transport) proxies requests to the existing REST API.

- Add src/mcp-server.ts with 6 tools: spawn_agent, list_agents,
  get_agent_status, get_agent_result, send_agent_message, cancel_agent
- Remove src/spawn-detector.ts and all references in session.ts/server.ts
- Add CLAUDEMAN_API_URL env var propagation to sessions and screens
- Write .mcp.json to case directories during creation
- Remove spawn1337 tag documentation from case-template.md
- Add claudeman-mcp bin entry to package.json

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -5,10 +5,11 @@
   "type": "module",
   "main": "dist/index.js",
   "bin": {
-    "claudeman": "./dist/index.js"
+    "claudeman": "./dist/index.js",
+    "claudeman-mcp": "./dist/mcp-server.js"
   },
   "scripts": {
-    "build": "tsc && chmod +x dist/index.js && mkdir -p dist/web dist/templates && cp -r src/web/public dist/web/ && cp src/templates/case-template.md dist/templates/",
+    "build": "tsc && chmod +x dist/index.js dist/mcp-server.js && mkdir -p dist/web dist/templates && cp -r src/web/public dist/web/ && cp src/templates/case-template.md dist/templates/",
     "start": "node dist/index.js",
     "dev": "tsx src/index.ts",
     "web": "node dist/index.js web",
@@ -36,6 +37,7 @@
   "license": "MIT",
   "dependencies": {
     "@fastify/static": "^8.0.0",
+    "@modelcontextprotocol/sdk": "^1.25.3",
     "chalk": "^5.3.0",
     "commander": "^12.1.0",
     "fastify": "^5.1.0",
@@ -44,7 +46,8 @@
     "ink-text-input": "^6.0.0",
     "node-pty": "^1.1.0",
     "react": "^19.2.3",
-    "uuid": "^10.0.0"
+    "uuid": "^10.0.0",
+    "zod": "^4.3.6"
   },
   "devDependencies": {
     "@types/node": "^20.14.0",