Address gosec security warnings (bd-102)

- Enable gosec linter in .golangci.yml
- Tighten file permissions: 0755→0750 for directories, 0644→0600 for configs
- Git hooks remain 0700 (executable, user-only access)
- Add #nosec comments for safe cases with justifications:
  - G204: Safe subprocess launches (git show, bd daemon)
  - G304: File inclusions with controlled paths
  - G201: SQL formatting with controlled column names
  - G115: Integer conversions with controlled values

All gosec warnings resolved (20→0). All tests passing.

Amp-Thread-ID: https://ampcode.com/threads/T-d7166b9e-cbbe-4c7b-9e48-3df36b20f0d0
Co-authored-by: Amp <amp@ampcode.com>

internal/storage/sqlite/events.go

@@ -58,6 +58,7 @@ func (s *SQLiteStorage) GetEvents(ctx context.Context, issueID string, limit int
 		args = append(args, limit)
 	}
 
+	// #nosec G201 - safe SQL with controlled formatting
 	query := fmt.Sprintf(`
 		SELECT id, issue_id, event_type, actor, old_value, new_value, comment, created_at
 		FROM events