Add .gitignore to .beads directory during init (#64)

- Create .gitignore file in .beads/ when running bd init
    - Ignores *.db and *.db-* patterns to prevent database commits
    - Add test coverage to verify .gitignore creation
    - Add .claude/settings.local.json to project .gitignore

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

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

Co-authored-by: Ben Madore <madorb@users.noreply.github.com>

README.md

@@ -774,16 +774,9 @@ Each line is a complete JSON issue object:
 
 ### Setup
 
-Add to `.gitignore`:
-```
-.beads/*.db
-.beads/*.db-*
-```
-
-Add to git:
-```
-.beads/issues.jsonl
-```
+The `.beads/` directory is automatically configured during `bd init`:
+- Database files (`.beads/*.db`, `.beads/*.db-*`) are gitignored automatically
+- JSONL file (`.beads/issues.jsonl`) is tracked in git
 
 ### Workflow