Unify agent and generator config to muse.{source}.{name} context pattern
- Rename context pattern from agent.* to muse.* across all files
- Add key_to_context() utility in think/utils.py for DRY conversion
- Fix bug: app generators now get correct muse.{app}.{name} context
- Move user overrides from journal.json.agents to providers.contexts
- Add /api/generators compatibility layer for settings UI
- Update docs (CORTEX.md, JOURNAL.md, PROVIDERS.md) with new patterns
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>