bug(goal-loop): one loop with an unknown phase moves goal-loop.json aside and loses every loop #1248

Found by the read-only C5 hunt (quality loop, 2026-09-25, temp/quality-loop/hunt-c5.md). The failure sequence is from the code; the loop has not yet verified it end to end. Verify before fixing.

GoalLoopStore (:61-81) throws when !Object.values(loops).every(validLoop), and renames the file to .corrupt. GoalLoopService.start() then starts empty (:232), and the next write makes the loss permanent. This is reachable by a newer build's phase or reason followed by a downgrade.

Expected: keep valid loops, and set only the unknown ones aside.