Merge fix workflow - move conflict resolution into the first workflow

[matthewp]

Changes

• Moves conflict resolution and changeset cleanup into the merge-main-to-next action so the branch is clean and buildable before CI runs. AI only runs when there are actual conflicts; clean merges skip it entirely.
• Strips the merge-fix action down to just test fixing — no more conflict stripping, no --no-frozen-lockfile. Uses --frozen-lockfile since the lockfile is already correct.
• Adds critical rules to the fix-tests skill based on analysis of a 1-hour timeout: never run pnpm install, time-box investigation to 5 min, diff before deep-reading source, batch bash commands.

Testing

• No test changes — these are CI workflow and skill instruction changes.

Docs

• No docs needed — internal CI automation only.

[changeset-bot]

⚠️ No Changeset found

Latest commit: e89a088

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