feat(ui): explicit Deny semantics with 2-denial hard-filter escalation (Sprint 8)

User policy decision (2026-06-05, exact): 'Hard filter. If it is denied
this week twice, it should be considered denied for good.'

The planner had no cross-week memory of denials: a denial on
meal_plan_item.approval_status was never consulted by the planner,
and NeverSuggest (the per-family permanent blocklist) was empty for
the user. The 'Roasted Sweet Potato and Chickpea Bowl' the user
denied on 2026-05-15 was still in the planner's pool 3 weeks
later.

Implements C + Z (explicit two-button model + soft-decay +
hard-filter escalation):
- Approve: untouched.
- Deny this week (1st in 90d): denial_expires_at = now() + 90d.
- Deny this week (2nd in 90d, server-side auto-escalation):
  denial_expires_at = NULL + a NeverSuggest row written.
- Never again (explicit): same as the 2nd-time auto-escalation.

Both soft and permanent denials are hard filters in the planner
(per user). A denied recipe never reappears until either the 90d
window expires or the user un-blocks via the NeverSuggest API.

Changes:
- Migration 0016: meal_plan_item.denial_expires_at (partial index)
  and meal_plan_vote.denial_scope.
- 3 backend helpers (_apply_denial, _ensure_never_suggest_recipe,
  _has_prior_active_soft_denial) — single source of truth for the
  deny path.
- POST /api/meals/items/{id}/deny?scope=this_week|never_again
  (default this_week). Returns promoted_to_permanent.
- POST /api/meals/vote/{id} extended: vote=approve|deny|never_again.
  Returns denial_scope + promoted_to_permanent.
- GET /api/meals/vote/{id} HTML page renders 3 buttons; supports
  one-click ?scope=... for email direct-action links.
- Email template (step_email): 3 direct-action links per recipe
  plus a secondary 'open vote page' link.
- Planner: _load_blocklists returns 3 sets; soft_denied_recipes
  is hard-filtered (union with blocked_recipes at the call site).
- Frontend: MealCard renders 3 buttons (Approve / Deny this week
  / Never again) for pending items. handleDeny is scope-aware;
  toast reflects promoted_to_permanent. window.confirm on
  'Never again' prevents accidental permanent blocks.

Verification:
- npm run build green.
- 21/21 planner tests pass (1 pre-existing test_filter_blocks_by_cost
  failure is NOT introduced by Sprint 8 — verified via git stash).
- Review/sprint8-verification.md: 11-step browser smoke + 4 API
  curls + email-render procedure + rollback.

Files:
- backend/alembic/versions/0016_denial_decay_and_scope.py (new)
- backend/app/models/__init__.py:221-242, 250-269
- backend/app/schemas/__init__.py:204-219, 248-269
- backend/app/api/meals.py:30-138 (helpers), 240-330 (HTML page),
  380-455 (submit_vote), 486-552 (deny_meal_item)
- backend/app/services/orchestrator/steps.py:283-300
- backend/app/services/planner/generate.py:59-99, 150-194
- frontend/src/api/index.ts:48-58
- frontend/src/pages/Dashboard.tsx:38-50, 385-410
- Review/{sprint8-verification,ui-nielsen-audit,handoff-ui-audit}.md
- fix-ui-audit.md
- docs/HANDOFF.md
- .agent/{plan,context}.md

Deploy (user runs on deployment host):
  cd ~/MealPlanner && git pull
  docker compose exec backend alembic upgrade head
  docker compose -f docker-compose.yml up -d --build backend frontend

backend/app/models/__init__.py

@@ -229,6 +229,10 @@ class MealPlanItem(Base):
     approval_status = Column(SQLEnum(MealPlanItemStatus, name="meal_plan_item_status_enum", create_type=False, values_callable=lambda obj: [e.value for e in obj]), default=MealPlanItemStatus.pending)
     denial_reason = Column(SQLEnum(DenialReason, name="denial_reason_enum", create_type=False, values_callable=lambda obj: [e.value for e in obj]))
     denial_details = Column(Text)
+    # Sprint 8: when this denial stops being a "soft" signal. NULL means
+    # either an approve / a non-denial row, or a "Never again" denial
+    # (no decay; promoted to NeverSuggest).
+    denial_expires_at = Column(DateTime(timezone=True), nullable=True)
     estimated_cost = Column(Numeric(10, 2))
     score = Column(Float)
     components = Column(JSONB)
@@ -254,6 +258,10 @@ class MealPlanVote(Base):
     meal_plan_item_id = Column(UUID(as_uuid=True), ForeignKey("meal_plan_item.id", ondelete="CASCADE"))
     family_member_id = Column(UUID(as_uuid=True), ForeignKey("family_member.id", ondelete="CASCADE"))
     vote = Column(Boolean, nullable=False)
+    # Sprint 8: which deny-scope the voter chose. NULL for approve votes.
+    # "this_week" = soft denial, decays in 90d. "never_again" = hard block
+    # (a NeverSuggest row is also written for permanence).
+    denial_scope = Column(String(16), nullable=True)
     voted_at = Column(DateTime(timezone=True), server_default=func.now())
 
     __table_args__ = (