fix(mcp): address 14 audit findings across MCP module (#1094)

* fix(mcp): address 14 audit findings across MCP module

- Replace panicking assert! in new_with_config with Result return (Critical)
- Fix initialize() race condition using tokio::sync::OnceCell (High)
- Fix localhost check bypass via proper URL parsing (High)
- Extract shared stream_transport_send() to deduplicate stdio/unix send logic
- Use atomic write (tmp+rename) for config file persistence
- Filter SSE responses by request_id to prevent wrong-response dispatch
- Share a single reqwest::Client for OAuth via fallible OnceLock
- Log notification send errors instead of silently discarding
- Fix unwrap_or(0) that could steal id=0 responses
- Store InitializeResult in OnceCell so callers can access server capabilities
- Add redirect logging in OAuth discovery
- Reuse is_localhost_url() in auth.rs
- Add McpToolWrapper unit tests and regression tests
- URL-encode PKCE challenge for consistency

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore: retrigger CI with skip-regression-check label

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: ilblackdragon

tests/e2e/scenarios/test_mcp_auth_flow.py

@@ -240,6 +240,7 @@ async def test_mcp_400_activate_triggers_auth(ironclaw_server, mock_llm_server):
         "/api/extensions/mock-mcp-400/activate",
         timeout=30,
     )
+    assert r.status_code == 200, f"Activate returned {r.status_code}: {r.text[:300]}"
     data = r.json()
 
     # The 400 should be treated as auth-required, returning an auth_url