docs(review): Sprint 6 verification log + plan/handoff/audit updates

Sprint 6 (F3 + F4) is now documented across the project:

- Review/sprint6-verification.md: new deploy + smoke-check doc.
  Backend + frontend deploy (no migration). 5 smoke-check
  sections: A) ShoppingList bulk-add end-to-end, B) F3 partial-
  failure edge case, C) F4 'Plan the week' button + dropdown,
  D) F4 edge cases (no empty slots, all recipes used, invalid
  meal_types), E) Sprints 1-5 regression spot-check. Rollback
  section covers revert (no migration to undo).

- fix-ui-audit.md: new Sprint 6 section (S6.1 F3, S6.2 F4,
  S6.3 verification gate). 'Done when' block updated to 6
  sprints / 10 commits / 20 findings closed.

- Review/handoff-ui-audit.md: updated to a 6-sprint cycle. TL;DR
  table includes the 8ad4ef6 row. File list includes sprint6-
  verification.md. File-level diff summary gains 8 new rows for
  Sprint 6 (F3 backend + F4 backend + 3 new schemas + 2 api
  bindings + 2 page changes). §Future list now strikethroughs
  F3 and F4. Follow-up tickets section added: the no-op
  'Generate Meal Plan' empty-state CTA, the (now-narrower) Pantry
  bulk-add ticket, and the 'Sprints 2-5 + Sprint 6 separate
  batch' deploy note.

- Review/ui-nielsen-audit.md: new Sprint 6 status block at the
  top. F3 + F4 documented with the design-decision context
  (ShoppingList-only scope; dropdown for All/Dinners; partial-
  success with detailed report).

- docs/HANDOFF.md: Last-updated line bumped to 6 sprints / 10
  commits / 20 findings / 6 §Future items. Header commit list
  gains the 8ad4ef6 row. New 'Sprint 6' subsection in the
  2026-06-04 session block. Commit table gained the 8ad4ef6 row.
  Files-modified + Files-added lists updated.

No code changes; the 3 pre-existing WIP files (backend/app/api/
recipes.py, schemas/recipe.py, nginx/nginx.conf) are deliberately
not staged.

Review/ui-nielsen-audit.md

@@ -76,6 +76,12 @@ The app looks polished on the surface (Tailwind palette, clean cards, working to
 > - **CRITICAL 0015 cast fix** (also in `d78bd18`): the CASE expression in `0015_normalize_pantry_aisles.py` failed with `text = boolean` on the `varchar(100) aisle` column. Sprint 2's dry-run query used a different path so the bug was not caught during Sprint 2. The fix is an explicit `::varchar(100)` cast on the whole CASE expression + simplified `WHEN '' THEN NULL` branch. **Without this fix, the deployment host's `alembic upgrade head` would have failed**, blocking Sprints 2, 3, 4 from going live. The local dev DB has been migrated successfully as of 2026-06-04.
 > - **Backend changes:** `meals.py` and `shopping_list.py` (new query param) + `0015_normalize_pantry_aisles.py` (cast fix).
 > - **Verification log:** `Review/sprint5-verification.md`. Deploy is a single batch for Sprints 2-5: backup → migrate → rebuild backend + frontend.
+>
+> **Sprint 6 status (commit `8ad4ef6`, awaiting deploy):** Two §Future items, both with design decisions captured in the commit message.
+> - **F3** Bulk 'add checked to pantry' on ShoppingList. Backend `POST /api/pantry/bulk` accepts `{items: HomePantryCreate[]}` and returns per-item status (`added` / `updated` / `skipped`) with totals. Per-item failure model: unknown ingredient → `skipped` with reason, not a 4xx. Frontend ShoppingList gains a primary `Add N to pantry` button next to the existing Reset button; toast reports `added X, updated Y, skipped Z`; only the items that actually landed are removed from the checked Set. **Scope decision:** ShoppingList only (the checked Set was the natural substrate; Pantry would need new multi-select UI).
+> - **F4** Plan the whole week on Dashboard. Backend `POST /api/meals/{id}/fill-empty-slots` with body `{meal_types: [str, ...]}` returns `FillEmptySlotsResult { filled: [{day, meal_type, item}], failed: [{day, meal_type, reason}] }`. Iterates day 1..7 in order; skips already-occupied slots; picks a recipe (prefer un-used, fall back to any) and inserts as `pending`. Per-slot failure model — never aborts mid-batch. Frontend Dashboard gets a primary `Plan the week` button (next to the Sprint 5 week-nav control) with a dropdown: `Dinners only` / `All meals`. Toast reports partial-success precisely: `Planned 12 of 21 meal slots — 9 failed (e.g. <reason>)`.
+> - **Backend changes:** `pantry.py` + `meals.py` (new endpoints) + `schemas/__init__.py` (3 new schema types).
+> - **Verification log:** `Review/sprint6-verification.md`. No migration. Deploy is `docker compose up -d --build backend frontend`.
 
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