fix: support Codex MCP import from TOML config

[npo-mmenke]

Problem

pi-mcp-adapter currently imports Codex MCP servers from ~/.codex/config.json
and expects them under mcpServers.

In current Codex installations, MCP servers are stored in
~/.codex/config.toml under [mcp_servers.<name>] instead.

That means Pi's imports: ["codex"] does not pick up MCP servers from a
modern Codex setup, even though codex mcp list shows them correctly.

What this changes

• prefer ~/.codex/config.toml when importing Codex MCP config
• read Codex TOML entries from mcp_servers
• fall back to ~/.codex/config.json / mcpServers for backward compatibility
• continue to the JSON fallback if config.toml exists but is invalid
• surface warnings during provenance/import parsing instead of silently swallowing them

Tests

Added coverage for:

• importing Codex MCP servers from TOML
• falling back to JSON when TOML is absent
• falling back to JSON when TOML is invalid
• provenance behavior for invalid TOML fallback

Verification

• npm test -- __tests__/config-imports.test.ts
• npm test