fix: checkpoint WAL on database dispose

[mortenoh]

Summary

Add WAL checkpoint before disposing SQLite file-based databases to ensure data is flushed to disk.

Problem

When using SQLite WAL mode:

• Data stays in WAL buffer and isn't flushed to the main database file
• External readers (like CLI tools) can't see committed data while service is running
• Service may hang on shutdown waiting for WAL to flush

Solution

Override dispose() in SqliteDatabase to execute PRAGMA wal_checkpoint(TRUNCATE) before closing the database engine. This:

• Flushes all WAL data to the main database file
• Truncates the WAL file to zero bytes
• Allows external readers to see all committed data
• Enables clean shutdown

Changes

• src/servicekit/database.py: Add dispose() override with WAL checkpoint
• tests/test_database.py: Add test for WAL checkpoint behavior
• pyproject.toml: Bump version to 0.6.0

Test plan

• Existing tests pass
• New test verifies WAL is checkpointed on dispose
• Manual test: chapkit CLI can read database while service running

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/servicekit/database.py	75.00%	2 Missing ⚠️

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