fix(mcp): refresh and discover provider servers

[astyfx]

Summary

• refresh Claude sessions and Codex App Server only when MCP config fingerprints change
• scope refresh state by provider configuration/workspace and defer Codex restart until active turns finish
• add read-only MCP discovery for Claude and Codex settings in Settings → MCP
• keep secrets and command details out of the renderer response

Validation

• bun test tests/mcp-discovery.test.ts tests/mcp-config-refresh.test.ts
• bun test tests/mcp-config-refresh.test.ts tests/codex-app-server-runtime.test.ts tests/claude-sdk-runtime.test.ts
• bun run typecheck
• bun run build:desktop