feat(coding-agent): added internal URL completion with async handlers
- Added internal URL completion types and router support for async scheme completion handlers.
- Implemented `complete()` for local, memory, agent, artifact, omp, rule, and skill handlers with robust completion fallbacks.
- Added internal URL autocomplete flow with context extraction, fuzzy matching, ranking, and a 25-item suggestion cap.
- Integrated internal URL completion into prompt and editor autocomplete behaviors and added completion tests.