Complete NextSteps roadmap: planning engine UI, calendar cluster, flexible wishes

Works through every numbered item in NextSteps260913.md section 3, plus the
three known verification issues in section 4.1.

Surface what the backend already computed:
- 3.1 render surplus_advice in PlanResults, mirroring the shortfall remedies
- 3.2 surface VacationBalance.is_assumed so assumed statutory years are visible
- 3.3 age-4 expiry given the proposed plan, via a new Age4Projection reusing
  the existing _age4_projections arithmetic (Dashboard stat verified, not rebuilt)

Calendar cluster (one pass over the holiday data):
- new GET /api/calendar/days exposing roda dagar, klamdagar and day overrides,
  paginated four years at a time
- 3.4 shade roda dagar/klamdagar, with R/K badges so colour is not the only signal
- 3.6 click-to-override behind an explicit mode toggle, leaving drag multi-select intact
- 3.7 click month/year to advance
- 3.8 per-year red-days list in Settings, statutory days plus overrides

i18n:
- 3.5 five backend-generated Swedish surfaces converted to message_key + data,
  following the tips_service pattern; old string fields replaced, not kept

Flexible wishes (3.9):
- PLANNING_ENGINE_SPEC section 10: window_mode, candidate search, cost function,
  deterministic tie-break, two-pass ordering, test matrix rows 15-24
- backend: entity, migration 006, _FULL_SCHEMA sync, repository, allocator
- frontend: season-preset toggle in WishEditor, unplaced outcome rendering

Fixes (4.1):
- pin typecheck to the local tsc rather than npx resolving a newer TypeScript
- ignore generated coverage/ and dist/ in the ESLint flat config
- fix the flaky usePlanApply test properly, with waitFor rather than a retry

Tests: backend 361 -> 404, frontend 540 -> 704. Coverage 89.47% -> 96.52% lines.

Not yet verified in a browser.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RXMhc9nT6sNz1SL4j8dznL

backend/app/utils/tip_predicates.py

@@ -9,13 +9,13 @@ from __future__ import annotations
 
 from datetime import date, timedelta
 
-import holidays
 from dateutil.relativedelta import relativedelta
 
 from app.config import settings
 from app.entities.child import Child
 from app.entities.personal_data import PersonalData
 from app.entities.planned_leave import PlannedLeaveDay
+from app.utils.holidays import is_non_working_day
 
 
 def weekly_intensity(planned_days: list[PlannedLeaveDay], period_weeks: float) -> float:
@@ -90,21 +90,23 @@ def sgi_at_risk(
 def red_day_clusters_in_range(
     from_date: date, to_date: date, year: int | None = None
 ) -> list[tuple[date, date]]:
-    """Return (start, end) pairs for clusters of ≥2 consecutive public holidays.
+    """Return (start, end) pairs for clusters of ≥2 consecutive non-working days.
 
-    Uses the `holidays` library (Sweden locale). A "cluster" is any stretch
-    where consecutive days are either weekends or public holidays. Useful for
-    the red-day wrapping tip.
+    Uses `app.utils.holidays.is_non_working_day` — the single source of truth
+    for "is this day free" (calendar cache + `holidays` library fallback),
+    so weekends, public holidays AND de facto days (julafton, midsommarafton,
+    nyårsafton, ...) all count. `year` is accepted for backward compatibility
+    but unused: `is_non_working_day` resolves each date's own year, so a
+    range spanning a year boundary is handled correctly without it.
     """
-    target_year = year or from_date.year
-    se_holidays = holidays.Sweden(years=target_year)
+    del year  # unused — is_non_working_day resolves per-date
 
     clusters: list[tuple[date, date]] = []
     cluster_start: date | None = None
 
     current = from_date
     while current <= to_date:
-        is_holiday = current in se_holidays or current.weekday() >= 5
+        is_holiday = is_non_working_day(current)
         if is_holiday:
             if cluster_start is None:
                 cluster_start = current