Add comprehensive test coverage for auto-flush feature

Implements bd-42: Add test coverage for auto-flush feature

Created cmd/bd/main_test.go with 11 comprehensive test functions:
- TestAutoFlushDirtyMarking: Verifies markDirtyAndScheduleFlush() marks DB as dirty
- TestAutoFlushDisabled: Tests --no-auto-flush flag disables feature
- TestAutoFlushDebounce: Tests rapid operations result in single flush
- TestAutoFlushClearState: Tests clearAutoFlushState() resets state
- TestAutoFlushOnExit: Tests flush happens on program exit
- TestAutoFlushConcurrency: Tests concurrent operations don't cause races
- TestAutoFlushStoreInactive: Tests flush skips when store is inactive
- TestAutoFlushJSONLContent: Tests flushed JSONL has correct content
- TestAutoFlushErrorHandling: Tests error scenarios (permissions, etc.)
- TestAutoImportIfNewer: Tests auto-import when JSONL is newer than DB
- TestAutoImportDisabled: Tests --no-auto-import flag disables auto-import

Coverage results:
- markDirtyAndScheduleFlush: 100%
- clearAutoFlushState: 100%
- flushToJSONL: 67.6%
- autoImportIfNewer: 66.1% (up from 0%)

All tests pass. Auto-flush feature is now thoroughly tested.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.beads/bd.jsonl

@@ -34,7 +34,7 @@
 {"id":"bd-4","title":"Add demo GIF/video showing bd quickstart in action","description":"Record asciinema or create animated GIF showing the full workflow","status":"open","priority":2,"issue_type":"feature","created_at":"2025-10-12T10:50:49.500051-07:00","updated_at":"2025-10-13T23:26:35.811831-07:00","dependencies":[{"issue_id":"bd-4","depends_on_id":"bd-8","type":"parent-child","created_at":"2025-10-12T10:51:08.399915-07:00","created_by":"stevey"}]}
 {"id":"bd-40","title":"Make auto-flush debounce duration configurable","description":"flushDebounce is hardcoded to 5 seconds. Make it configurable via environment variable BEADS_FLUSH_DEBOUNCE (e.g., '500ms', '10s'). Current 5-second value is reasonable for interactive use, but CI/automated scenarios might want faster flush. Add getDebounceDuration() helper function. Located in cmd/bd/main.go:31.","status":"open","priority":3,"issue_type":"feature","created_at":"2025-10-13T22:35:06.126282-07:00","updated_at":"2025-10-13T23:26:35.81192-07:00"}
 {"id":"bd-41","title":"Add godoc comments for auto-flush functions","description":"Add comprehensive godoc comments for findJSONLPath(), markDirtyAndScheduleFlush(), and flushToJSONL() explaining behavior, concurrency considerations, and error handling. Include notes about debouncing behavior (timer resets on each write, flush occurs 5s after LAST operation) and flush-on-exit guarantees. Located in cmd/bd/main.go:188-307.","status":"open","priority":4,"issue_type":"chore","created_at":"2025-10-13T22:35:13.518442-07:00","updated_at":"2025-10-13T23:26:35.811999-07:00"}
-{"id":"bd-42","title":"Add test coverage for auto-flush feature","description":"Add comprehensive tests for auto-flush functionality:\\n- Test that markDirtyAndScheduleFlush() is called after CRUD operations\\n- Test debounce timing (rapid operations result in single flush)\\n- Test --no-auto-flush flag disables feature\\n- Test flush on program exit\\n- Test concurrent operations don't cause races\\n- Test error scenarios (disk full, permission denied, etc.)\\n- Test import command triggers auto-flush\\n\\nCurrent implementation has no test coverage for the auto-flush feature. Located in cmd/bd/main_test.go (to be created).","status":"open","priority":2,"issue_type":"task","created_at":"2025-10-13T22:35:22.079794-07:00","updated_at":"2025-10-13T23:26:35.81208-07:00"}
+{"id":"bd-42","title":"Add test coverage for auto-flush feature","description":"Add comprehensive tests for auto-flush functionality:\\n- Test that markDirtyAndScheduleFlush() is called after CRUD operations\\n- Test debounce timing (rapid operations result in single flush)\\n- Test --no-auto-flush flag disables feature\\n- Test flush on program exit\\n- Test concurrent operations don't cause races\\n- Test error scenarios (disk full, permission denied, etc.)\\n- Test import command triggers auto-flush\\n\\nCurrent implementation has no test coverage for the auto-flush feature. Located in cmd/bd/main_test.go (to be created).","status":"closed","priority":2,"issue_type":"task","created_at":"2025-10-13T22:35:22.079794-07:00","updated_at":"2025-10-13T23:36:28.90411-07:00","closed_at":"2025-10-13T23:36:28.90411-07:00"}
 {"id":"bd-43","title":"Test auto-sync feature","description":"","status":"closed","priority":2,"issue_type":"task","created_at":"2025-10-13T22:47:41.738165-07:00","updated_at":"2025-10-13T23:26:35.812171-07:00","closed_at":"2025-10-13T22:48:02.844213-07:00"}
 {"id":"bd-44","title":"Regular auto-ID issue","description":"","status":"closed","priority":2,"issue_type":"task","created_at":"2025-10-13T23:16:29.970089-07:00","updated_at":"2025-10-13T23:26:35.812252-07:00","closed_at":"2025-10-13T23:16:45.231439-07:00"}
 {"id":"bd-45","title":"Test flush tracking","description":"","status":"closed","priority":2,"issue_type":"task","created_at":"2025-10-13T23:22:18.472476-07:00","updated_at":"2025-10-13T23:26:35.812337-07:00","closed_at":"2025-10-13T23:22:31.397095-07:00"}