skills/book-gig: auto-detect email bounces during reply scan and toggle outreach-ineligible

[JoshuaVSherman]

Child of web-jam-tools#875 ("book-gig skill phase 2 enhancements (Epic)").

What this builds

Enhances the response tracking pipeline (deno task book-gig --replies / src/book-gig/replies.ts) and backend reply detection to automatically identify email delivery failures (Mail Delivery Subsystem, 550 User unknown, Address not found, or SMTP bounce notifications) and automatically update the corresponding venue record via PATCH /venue/:id with outreachEligible: false and a timestamped note detailing the bounce.

1. Updates reply classifier in src/book-gig/ to recognize bounce notifications and associate them with the original recipient venue.
2. Calls PATCH /venue/:id to set outreachEligible: false and record the bounce in notes, preventing dead emails from entering subsequent candidate pools.
3. Surfaces a prominent [BOUNCE DETECTED] warning in the replies status table.
4. Adds automated unit tests covering bounce email parsing and automated venue eligibility updating.

Acceptance criteria

1. When --replies detects a bounce notification for a venue, that venue is updated in MongoDB with outreachEligible: false.
2. Bounced venues are highlighted in the --replies status table and review artifacts.
3. deno task test, deno task fmt:check, deno task lint, and deno task sast pass 100% green.