Add /display Finish footer with co-equal Save Deck/Print + save-before-PDF draft backup (#275)

[WilfordGrimley]

Summary

Implements issue #275 (proposal-h-display-layout-spec.md ADDENDUM D9/D10): the /display right-rail Finish footer and the save-before-PDF hard constraint ("save deck should come before PDF completes because we have to rely on clients available mem for the PDF").

• FinishFooter.tsx — replaces the old three-button "Prepare Print" stack (Export ▾ / Save PDF to Google Drive / Generate PDF) with two co-equal btn-primary buttons (Save Deck, Print / Export →) plus the unchanged Export ▾, and a compact "✓ Draft backed up locally" note. Anonymous sessions get a "Sign in to Save" link in place of Save Deck (server save is authenticated-only by construction).
• useProjectDraftBackup.ts (F1) — silent, debounced localStorage mirror of the working project (indexes/settings only, never image pixels — the governing "we index, we do not store images" premise applied to this browser's own disk). Offers a restore nudge on the empty-project landing when a prior session's draft outlives an emptied project, and fires the D9(2) promotion nudge post-import (reusing the existing Toasts system, no new UI surface).
• PrePrintSaveGate.tsx (F3) — runs the D9(3) sequence when "Print / Export →" is pressed: flush the draft synchronously → if authenticated AND dirty, show a lightweight "Save before printing?" prompt (Save/Skip) → only then client-side-navigate to the new Print page. Saving gates PDF; PDF never gates saving.
• useSaveDeckFlow.tsx — extracted from SavedDeckPanel.tsx's own passphrase-setup/unlock/save modal chain so the footer's Save Deck button and the pre-print gate's Save choice reuse it without forking; SavedDeckPanel.tsx itself now rides the same hook, unchanged behavior.
• pages/print.tsx (D10/F5) — new thin route wrapper mounting the unchanged FinishedMyProject, mirroring pages/myDecks.tsx. /display's own inline PDF export pipeline (Item 2's useDownloadPDF/useSaveToDrivePDF/ImageFailureConfirmModal/fetch-progress bar) is removed outright — PDF generation now lives solely on this Print page.

Deviations from spec (documented, not silently accepted)

1. D10's tab reorder + PDF-tab preview removal deferred. The owner addendum on D10 (reorder to PDF · MakePlayingCards · NotMPC · PringlePrints with PDF default, and dropping the PDF tab's own preview) is explicitly out of this issue's scope per the task — pages/print.tsx mounts FinishedMyProject unchanged. Tracked as its own follow-up in the spec doc.
2. Settings-parity gap, left open. /display's own Page Setup controls (paper size/bleed edge/guides — plain component state) don't carry over to the Print page's classic PDFGenerator, which has always had separate settings and doesn't read this page's margin-profile/card-spacing redux slices either. Out of scope for D9/D10 (save-vs-print ordering + route linkage, not settings portability) — documented in the spec doc and in DisplayPage.tsx's own module comment.
3. DisplayPageExport.spec.ts deleted (not selector-updated) since its subject — the page's own inline PDF pipeline — no longer exists; PDFGenerator.spec.ts already covers the underlying pipeline mechanics unchanged. PostExportContributionPrompt.spec.ts's "- /display" describe block removed for the same reason; its "classic Print! tab" block is untouched.
4. docs_lint allowlist entries removed for useProjectDraftBackup.ts/pages/print.tsx now that both files exist — lint passes naturally.

Test plan

• tsc --noEmit clean
• npx eslint clean on all touched files
• npx prettier@2.7.1 --check clean on all touched files
• Jest: new useProjectDraftBackup.test.tsx (8 tests: empty-project no-op, flush writes indexes/settings only, debounced auto-write, restore-nudge surfacing, restore rehydration, dismiss-without-delete, post-import + pre-print promotion nudges) + full existing suite (59 suites / 504 tests, all green, including SavedDeckPanel.test.tsx unchanged after the useSaveDeckFlow extraction)
• Playwright: new DisplayFinishFooter.spec.ts (5 tests covering the full journey — anonymous sign-in-link + direct navigation, authenticated Save Deck button + draft-backed-up note, the full save-gate→unlock→SaveDeckModal→Print-page journey, Skip→Print-page, and the restore-nudge round trip) + PostExportContributionPrompt.spec.ts + DisplayPage.spec.ts + SavedDecks.spec.ts all green (four intermittent failures seen once under 4-worker parallel load — DisplayPage.spec.ts's own pre-existing phone-viewport scroll test plus three others — all confirmed to pass in isolation/on rerun; unrelated to this change, not touched by this PR)
• Manual UI walkthrough in a running dev server (deferred — this was verified via the Playwright journey above, which drives a real browser against the real components; no separate manual pass performed)

Open items

1. Wiki: /display usage documentation (if any exists) needs a note that the finish footer changed — flagging for the merge-time checklist since this is user-visible.
2. The settings-parity gap (deviation Promote PringlePrints to a full ordering tab #2 above) is a good candidate for a follow-up issue once D10's own tab-reorder work lands.

🤖 Generated with Claude Code