fix(docs): remove non-existent HTTP/SSE transport and MCP_SERVER_PORT

MCP server source confirms:
- Only StdioServerTransport exists (no HTTP/SSE server)
- No MCP_SERVER_PORT env var
- apiCall() sends no Authorization header

Removed the entire "Transport modes" section (non-existent HTTP/SSE
endpoint), MCP_SERVER_PORT row from env table and troubleshooting, and
MOLECULE_API_KEY from config examples (auth is planned, not wired yet).
Replaced with accurate "Transport" section documenting stdio-only mode.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

content/docs/mcp-server.mdx

@@ -42,6 +42,8 @@ For SaaS deployments, set `MOLECULE_URL` to your tenant URL:
 "MOLECULE_URL": "https://your-org.moleculesai.app"
 ```
 
+Auth via `MOLECULE_API_KEY` is planned for a future release.
+
 ### Verify
 
 Once configured, your MCP client should show 87 Molecule AI tools. Test with:
@@ -152,6 +154,11 @@ The MCP server exposes tools across these categories:
 | Variable | Default | Description |
 |---|---|---|
 | `MOLECULE_URL` | `http://localhost:8080` | Platform API URL |
+| `MOLECULE_API_KEY` | — | Bearer token for platform authentication (planned) |
+
+## Transport
+
+The MCP server uses **stdio transport** — the client (Claude Code, Cursor, etc.) spawns the server as a child process and communicates via JSON-RPC over stdin/stdout. Configure in your AI client's `mcp.json` as shown in Quick start above.
 
 ## Troubleshooting