v0.5.3 — transparent event compression + done-jobs retention

• Event content over 2048 characters is now stored lzma-compressed transparently, with byte-for-byte identical reads and roughly a third of the stored audit size; new events compress at write time and existing rows migrate in bounded, idempotent background batches at startup without blocking serving.
• Finished background queue rows older than 7 days are swept at startup; pending, running, and failed jobs are untouched.
• A corrupt stored blob fails loud rather than serving truncated audit data; large stores reclaim file space with one manual VACUUM (no automatic VACUUM).
• Stores that have run compression should not be reopened by a pre-compression build; re-upgrading restores full reads.