[codex] Sync special activity prompts

[Ridealist]

Summary

• Fill out the Special Activity Plan task card and fix the opening sentence.
• Align all four condition-combination prompts with the task-card source of truth for final sentence wording and Class 3/Class 5 facts.
• Add a regression test that catches future special activity prompt drift.

Validation

• pnpm prompts:check
• UV_CACHE_DIR=/tmp/uv-cache uv run python -m pytest agent/tests -q
• pnpm --dir client test
• pnpm run build
• git diff --check

Notes

• gh auth status reports the local GitHub CLI token is invalid, so this PR was opened through the GitHub connector.