feat(mcp): add provider server management

[astyfx]

Summary

Add end-to-end MCP server management for Claude and Codex, including OAuth recovery, native configuration CRUD, and per-server connection diagnostics.

Changes

Features

• mcp: add reviewed create, update, rename, and delete flows for Claude user/project/local configs and Codex user config
• mcp: add Claude OAuth parity and provider-specific connection status with recent sanitized errors
• settings: add accessible MCP management dialogs and provider/scope configuration rows
• docs: document MCP server management and the Registry discovery/install UX proposal

Fixes

• mcp: keep opaque credentials and command arguments out of renderer IPC while preserving compatible existing values
• mcp: reject stale previews and use atomic or provider-native writes

Test Evidence

• bun run test:ci
• Lens manual QA: add → review → apply, edit with protected values, delete confirmation, and focus/label semantics
• Theme guard files checked; no new theme tokens

Notes

• Codex CRUD is intentionally limited to the user configuration layer.
• Registry discovery/install remains a design proposal; manual CRUD is implemented in this PR.
• No breaking changes.

[heath-s]

Approved