Add local MCP server integration for Cap Desktop

[onyedikachi-david]

Add a local MCP server so AI clients can control Cap Desktop over HTTP or stdio.

Includes recording, screenshots, devices, files, diagnostics, authentication, session management, and MCP settings UI.

[linear]

CAP-736

[tembo]

PR #1942 already implements this feature and is currently open for review. The implementation includes:

• Desktop MCP server in apps/desktop/src-tauri/src/mcp.rs (~2000 lines): An Axum-based HTTP server exposing 40+ tools with bearer-token authentication and session management (30-minute TTL)
• CLI stdio shim in apps/cli/src/mcp.rs: cap mcp command that reads the MCP port/token from the desktop store and proxies JSON-RPC messages
• Settings UI in apps/desktop/src/routes/(window-chrome)/settings/cli.tsx: New MCP section in CLI settings for enabling/disabling the server, rotating tokens, and copying client configs

The PR has received a Greptile review with a few items worth addressing before merge:

1. Unknown tool names return -32602 (Invalid params) instead of an isError: true tool result, which may cause strict MCP clients to abort sessions
2. HTTP config preview renders literal null values when the server hasn't been enabled yet
3. Non-constant-time bearer token comparison (low practical risk since it's localhost-only)

Related: Issue #971 requests n8n AI agents integration, which could leverage this MCP server once merged.