fix(puzzles): merge anon progress, rehydrate completion, recover orphaned draft (#1650)

[jung-thomas]

Fixes the three puzzle bugs reported in #1650.

Bug 1 — anonymous answers dropped after signing in

resumeProgress (hugo-apps/src/puzzle/App.vue) did "server wins if the server grid is non-empty", silently discarding answers typed while logged out — those never reach the xsuaa-gated save endpoints, so on login the server grid (missing them) overwrote everything.

Fix: replace shouldMigrate with mergeProgress (lib/progress.ts): the server stays authoritative for cells it holds, but local-only answers (cells the server left blank) are preserved and persisted back.

Bug 2 — completion doesn't survive a page refresh

solved was only ever an in-memory ref; nothing re-read completion on load, so the solved banner + Reset button disappeared after refresh (re-clicking Check re-set it in memory — exactly the reported "Check again gives me credit + Reset").

Fix: PuzzleService.getProgress now returns a completed flag derived from the non-superseded PUZZLE TaskRecord (srv/puzzle-service.{cds,js}); the solver re-hydrates solved and paints the grid green on load (markSolvedFromServer). No answer key is shipped to the client.

Bug 3 — admin save fails with draftEdit HTTP 409: DRAFT_ALREADY_EXISTS

An orphaned edit draft left by a prior session made every subsequent save fail; the controller treated the 409 as fatal.

Fix: extract the draft save orchestration into app/admin/puzzles/webapp/lib/draft-save.js (unit-tested) and recover from that specific 409 by resuming the existing draft (a CAP edit draft shares the active entity's key) — PATCH it with the fresh fields and activate. Non-DRAFT_ALREADY_EXISTS 409s (e.g. locked by another user) still surface as errors.

Tests

• hugo-apps/src/puzzle/__tests__/progress.test.ts — mergeProgress (migrate, preserve local-only, server-wins-conflict, no-op, corrupt JSON).
• test/unit/puzzle-service-complete.test.js — getProgress reports completed true/false.
• test/unit/puzzle-draft-save.test.js (new) — 409 recovery, happy update/create paths, non-409 + non-DRAFT_ALREADY_EXISTS re-throw.
• Full unit project: 0 test failures (7805 passed). The 14 failed files are pre-existing worktree node_modules import gaps (graphology in app/explore), unrelated to this change.

Not deployed

Frontend + admin-UI changes here — per project rules the island bundle + admin bundle need a full npm run deploy (no --skip-build/-m), and the puzzle island fingerprint goes through build:island-manifest. This PR is code only.