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/services/day_override_service.py

@@ -0,0 +1,73 @@
+"""Business logic for day overrides.
+
+The service owns rules; the repository only persists. Routers call services,
+not repositories directly. Mirrors VacationDaysService's upsert-by-natural-key
+shape: a workspace has at most one override per date.
+"""
+
+from datetime import date, datetime
+from uuid import UUID, uuid4
+
+from app.entities.day_override import DayOverride
+from app.repositories.day_override_repository import DayOverrideRepository
+from app.utils.errors import NotFoundError, ValidationError
+
+
+class DayOverrideService:
+    def __init__(self, repo: DayOverrideRepository) -> None:
+        self._repo = repo
+
+    async def upsert(
+        self,
+        workspace_id: UUID,
+        day: date,
+        is_working_day: bool,
+        note: str | None = None,
+    ) -> DayOverride:
+        """Create or update the (workspace, date) override.
+
+        A service should not trust its caller even though the schema also
+        guards the note length.
+        """
+        if note is not None and len(note) > 280:
+            raise ValidationError("Day override note cannot exceed 280 characters")
+
+        existing = await self._repo.get_by_workspace_date(workspace_id, day)
+        if existing is not None:
+            existing.is_working_day = is_working_day
+            existing.note = note
+            return await self._repo.update(existing.id, existing)
+
+        entity = DayOverride(
+            id=uuid4(),
+            workspace_id=workspace_id,
+            date=day,
+            is_working_day=is_working_day,
+            note=note,
+            created_at=datetime.now(),
+            updated_at=datetime.now(),
+        )
+        return await self._repo.create(entity)
+
+    async def get(self, day_override_id: UUID) -> DayOverride:
+        entity = await self._repo.get_by_id(day_override_id)
+        if entity is None:
+            raise NotFoundError(f"DayOverride {day_override_id} not found")
+        return entity
+
+    async def list_for_workspace(self, workspace_id: UUID) -> list[DayOverride]:
+        return await self._repo.list_by_workspace(workspace_id)
+
+    async def delete(self, day_override_id: UUID) -> None:
+        await self._repo.delete(day_override_id)
+
+    async def get_effective_map(self, workspace_id: UUID) -> dict[date, bool]:
+        """Return {date: is_working_day} for every override in a workspace.
+
+        This is the shape `AllocationInputLoader` feeds into
+        `AllocationInput.day_overrides` — see
+        `app.services.allocation_service.is_free_day` for the single place
+        it's merged with the calendar.
+        """
+        overrides = await self._repo.list_by_workspace(workspace_id)
+        return {o.date: o.is_working_day for o in overrides}