refactor: unify event processing logic

Eliminates code duplication by extracting core event processing into
reusable functions. All state and PR event processing now uses the same
unified logic from src/git/process.rs.

Changes:
- Add src/git/process.rs with unified processing functions
  - process_state_with_git_data() for state events
  - process_pr_with_git_data() for PR events
  - Pure functions with comprehensive result types

- Refactor policy handlers to use unified processing
  - src/nostr/policy/state.rs: Remove ~70 lines of duplicated logic
  - src/nostr/policy/pr_event.rs: Remove ~40 lines of duplicated logic

- Refactor purgatory processing to use unified functions
  - src/git/sync.rs: Remove ~125 lines of duplicated logic
  - Make extract_owner_from_repo_path() public for reuse

Benefits:
- DRY: Single source of truth for event processing
- Testable: Pure functions with clear contracts
- Maintainable: Changes happen in one place
- Consistent: All code paths use same logic

All 217 unit tests + 40 integration tests pass (257/257).

0 files changed, 0 insertions, 0 deletions