fix: Auto-export to JSONL now works correctly [fixes #23]

Fixed bug where PersistentPostRun was clearing isDirty flag before
calling flushToJSONL(), causing the flush to abort immediately.

The fix ensures flushToJSONL() handles the isDirty flag itself,
allowing the JSONL export to complete successfully.

Also added Arch Linux AUR installation instructions to README.

Changes:
- cmd/bd/main.go: Fixed PersistentPostRun flush logic
- README.md: Added Arch Linux (AUR) installation section
- .beads/bd.jsonl: Auto-exported issue bd-169 (init -q flag bug)

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

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

README.md

@@ -71,6 +71,17 @@ go build -o bd ./cmd/bd
 sudo mv bd /usr/local/bin/  # or anywhere in your PATH
 ```
 
+#### Arch Linux
+
+```bash
+# Install from AUR
+yay -S beads-git
+# or
+paru -S beads-git
+```
+
+Thanks to [@v4rgas](https://github.com/v4rgas) for maintaining the AUR package!
+
 #### Windows 11
 For Windows you must build from source.
 Assumes git, go-lang and mingw-64 installed and in path.