feat: web access via MCP (Firecrawl search/scrape) + mcp server attach support

- agent/web_mcp.py: stdio MCP server exposing web_search and web_scrape,
  backed by the self-hosted Firecrawl stack on xNAS (no API key needed)
- agent.py: Agent now attaches mcp_servers built from config; EXTRA_MCP_SERVERS
  env var allows adding arbitrary HTTP/SSE MCP servers as JSON
- Dockerfile: installs livekit-agents[mcp], copies web_mcp.py
- .env.example: WEB_MCP_ENABLED, FIRECRAWL_BASE, EXTRA_MCP_SERVERS documented

.env.example

@@ -17,3 +17,14 @@ LIVEKIT_API_SECRET=devsecret
 
 # Web UI port
 WEB_PORT=8090
+
+# ── Web access (MCP tools: web_search + web_scrape) ────────────────────────
+# Backed by the self-hosted Firecrawl stack on xNAS.
+WEB_MCP_ENABLED=true
+FIRECRAWL_BASE=http://192.168.86.2:3002
+# Only needed if your Firecrawl instance requires an API key
+# FIRECRAWL_API_KEY=
+
+# Extra MCP servers (optional). JSON list of {url, transport} objects.
+# transport: "sse" | "streamable_http" | omit for auto-detect
+# EXTRA_MCP_SERVERS=[{"url":"http://192.168.86.2:3001/mcp","transport":"streamable_http"}]