Free days, vacation forfeiture, and global auto-replanning

Free days (Sat/Sun/red days, subject to DayOverride) can never be
vacation, and can only be parental leave when the workspace opts in via
take_pl_on_red_days. The allocator already honoured this; the hand-pin
path bypassed it entirely.

- PlanningService gains optional workspace_repo/day_override_repo deps
  and _reject_illegal_free_day, enforced in add_planned_day and update.
  Reuses allocation_service.is_free_day rather than re-deriving it, and
  no-ops when the deps are unset so existing callers are unaffected.
- update_planned_day had no ValidationError handler at all, so a
  validation failure there 500'd instead of 422'ing. Fixed.
- Calendar filters the pin write loop by the day's isFree; the modal
  explains free days stay off, and that pinning opts a day out of
  automatic re-planning.

Vacation days at risk of forfeiture were computed and sent over the
wire but never rendered: an at-risk column with the age-out/over-cap
split, and a dashboard key figure.

PlanProposal.warnings was likewise parsed but rendered nowhere, for all
three kinds. Adds PlanWarningCard in a Risks section above the tips,
with parent names resolved and dates formatted.

POST /api/plan/sync now fires from the workspace layer on every
plan-input change rather than only from Calendar, so a Settings edit or
a pinned-day save re-plans day types instead of merely refetching.
Overlapping bumps coalesce into one trailing run; a rejection cannot
wedge the in-flight guard. eviction_preview was silently dropped by the
frontend despite always being on the wire, and is now surfaced through
context.

Verified: backend 890 passed (91.49% coverage), frontend 1297 passed,
ruff/eslint/tsc clean. Browser-checked in Swedish and English.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JVQx4NUvPbJhn6UcvRd2QY

backend/app/routers/planned_days.py

@@ -19,6 +19,23 @@ def _to_response(day) -> PlannedLeaveDayResponse:
     return PlannedLeaveDayResponse.from_entity(day)
 
 
+def _to_http_error(exc: ValidationError) -> HTTPException:
+    """Map a `ValidationError` to a 422, forwarding its `message_key` + `data`
+
+    (§3.5) as structured `detail` when present — e.g. the free-day hand-pin
+    guard (`PlanningService._reject_illegal_free_day`) — so the frontend can
+    translate it instead of parsing an English sentence. Falls back to the
+    plain message for the (more common) error raised without one. Mirrors
+    `app.routers.workspace._to_http_error`.
+    """
+    if exc.message_key:
+        return HTTPException(
+            status.HTTP_422_UNPROCESSABLE_ENTITY,
+            detail={"message_key": exc.message_key, "data": exc.data},
+        )
+    return HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, detail=str(exc))
+
+
 @router.post("", response_model=PlannedLeaveDayResponse, status_code=status.HTTP_201_CREATED)
 async def create_planned_day(
     payload: PlannedLeaveDayCreate,
@@ -41,7 +58,7 @@ async def create_planned_day(
         )
         return _to_response(day)
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise _to_http_error(exc) from exc
 
 
 @router.get("", response_model=list[PlannedLeaveDayResponse])
@@ -96,6 +113,8 @@ async def update_planned_day(
         return _to_response(day)
     except NotFoundError as exc:
         raise HTTPException(status.HTTP_404_NOT_FOUND, str(exc)) from exc
+    except ValidationError as exc:
+        raise _to_http_error(exc) from exc
 
 
 @router.delete("/{planned_leave_day_id}", status_code=status.HTTP_204_NO_CONTENT)