Re-enable finishingbot.yml against gitbot-fleet (+ binary-name bug) #40

Sub-issue of #37.

finishingbot.yml clones the phantom hyperpolymath/finishing-bot. The bot lives in hyperpolymath/gitbot-fleet at bots/finishingbot. Two bugs: (1) phantom clone; (2) the crate's binary is finishing-bot (hyphenated, [[bin]] name = "finishing-bot") but the workflow runs finishingbot — so even a clone-swap stays red.

Fix: clone gitbot-fleet at a pinned SHA, cargo build --release in bots/finishingbot, run finishing-bot audit, drop if: false. No upstream change needed.

Refs #37.