contribute: Plan every instance arm before the first provision

Reviewers predictably ask for each touched path with its control, a database plan for any ActiveRecord update, and the read paths a customer uses. Found after teardown, each ask costs a second provision. Phase 5 now lists every arm at design time so one provision covers them, including mutation on the dev base and the captures a later MR needs.

The pre-scan replays the requested reviewer and maintainer from their own notes, and records a decision on any review Danger did not label. Commits meet the GitLab Duo review rules on the default branch, which Duo reviews against, before the first push.

Database plans come from Database Lab, run by a team member in the Postgres.ai web console, with the guide's local-plan form as the fallback. A multi-category MR whose author holds no maintainer role requests its reviewers in one wave once tests pass, and maintainers join through each reviewer's handoff.

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