Drop TODO.md's stale docs-only cache caveat (closes #421)

The Status paragraph said a docs-only commit replays from the layer
cache. Since the check workflow writes the commit hash into
.ci-fingerprint and the build context carries .git, every commit
invalidates the COPY layer and the checks run. README's "CI gate
honesty" section already says so, so the paragraph is removed rather
than restated.

Model: opus-5-5

TODO.md

@@ -40,12 +40,6 @@ duplicate. That is deliberate — the alternative is a silent lost
 delivery — and the README says so under Rationale. It is not a defect
 to re-file.
 
-One caveat on reading a green check: a docs-only commit deliberately
-replays from the layer cache
-(https://git.eeqj.de/sneak/webhooker/issues/119), so a green status on
-such a commit evidences a replay rather than an executed run. A code
-commit invalidates the `COPY` layer and genuinely executes.
-
 # Next Step
 
 Clear the rest of the open 1.0.0 milestone