Enhance .gitignore created during bd init (#98)

- Expand .gitignore to include all SQLite-related files (journal, WAL, SHM)
- Add daemon runtime files (logs, PID, socket)
- Include legacy database filenames
- Explicitly allow JSONL files with !*.jsonl pattern
- Add test coverage to verify .gitignore content

cmd/bd/testdata/init.txt

@@ -4,4 +4,10 @@ stdout 'initialized successfully'
 exists .beads/test.db
 exists .beads/.gitignore
 grep '^\*\.db$' .beads/.gitignore
-grep '^\*\.db-\*$' .beads/.gitignore
+grep '^\*\.db-journal$' .beads/.gitignore
+grep '^\*\.db-wal$' .beads/.gitignore
+grep '^\*\.db-shm$' .beads/.gitignore
+grep '^daemon\.log$' .beads/.gitignore
+grep '^daemon\.pid$' .beads/.gitignore
+grep '^bd\.sock$' .beads/.gitignore
+grep '^!\*\.jsonl$' .beads/.gitignore