Phase 2 of tab completion: semantic completion for session IDs.
Features:
- /resume <TAB> lists all available sessions from .g3/sessions/
- /resume abc<TAB> filters to sessions starting with 'abc'
- Gracefully returns empty if .g3/sessions/ doesn't exist
Implementation:
- Added list_sessions() helper method to G3Helper
- Added Case 4 in complete() for /resume command
- Updated module docs to reflect new capability
Tests:
- test_resume_completion_lists_sessions - verifies listing and filtering
- test_resume_completion_graceful_no_panic - verifies no crash without sessions dir
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