Addresses final-review findings: I1 render-generation guard prevents a double-mount
/timer leak on rapid re-navigation; I2 adds anonymous-rejection tests for the owner-only
POST /speedtest/run and /health/check; M1 CSS comment; M2 cron↔worker dedup note;
M4 full 8-byte PNG signature check; M5 card-contract unit test for all 7 cards.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
