Tagger: correcting an estimated capture time leaves the ESTIMATED marker in place

After #237, a file whose camera wrote no time uploads with `timestamp_issues` true in deployments.csv and a `[TIMESTAMP:]` marker in its media.csv comments. Fixing that time in the tagger rewrites the timestamp column only. The marker stays, so the file reopens with the ESTIMATED badge on a hand-corrected time, and `timestamp_issues` never flips back once every flagged file is corrected.

Where: `packages/camtrap/src/index.ts` `mergeMedia` writes col 4 and leaves col 10 alone.

Fix: when a correction lands on a flagged row, rewrite the marker to `manual` (or drop it), and recompute `timestamp_issues` when no flagged rows remain. Whether a hand-corrected time should still count as an issue is a team call, see item 1 in #237.