Remove submission email draft from repository

[batbrainy]

Removes recruiter-facing submission-email content while retaining the technical verification checklist.

Changes:

• Delete checklist section 8, including recipient, subject, body, signature, and send-record instructions.
• Remove email-template and send-step requirements from the implementation plan.
• Keep the reusable checklist, clean-checkout verification, and historical implementation context.

Validation:

• Repository-wide email-residue scan returns no matches.
• 23 Markdown files have balanced fences.
• 98 local links and anchors resolve.
• git diff --check passes.
• docker compose config --quiet passes.
• Only IMPLEMENTATION_PLAN.md and docs/SUBMISSION_CHECKLIST.md changed.