BE-CAL-API-002: Implement calendar day-view query API

- Add GET /calendar/day endpoint with optional ?date= query param
- Returns unified CalendarDayResponse merging real slots + virtual plan slots
- New CalendarSlotItem schema supports both real (id) and virtual (virtual_id) slots
- Excludes inactive slots (skipped/aborted) from results
- All slots sorted by scheduled_at ascending
- Helper functions for real/virtual slot conversion

app/schemas/calendar.py

@@ -2,6 +2,7 @@
 
 BE-CAL-004: MinimumWorkload read/write schemas.
 BE-CAL-API-001: TimeSlot create / response schemas.
+BE-CAL-API-002: Calendar day-view query schemas.
 """
 
 from __future__ import annotations
@@ -152,3 +153,46 @@ class TimeSlotCreateResponse(BaseModel):
     """Response after creating a slot — includes the slot and any warnings."""
     slot: TimeSlotResponse
     warnings: list[WorkloadWarningItem] = Field(default_factory=list)
+
+
+# ---------------------------------------------------------------------------
+# Calendar day-view query (BE-CAL-API-002)
+# ---------------------------------------------------------------------------
+
+class CalendarSlotItem(BaseModel):
+    """Unified slot item for day-view — covers both real and virtual slots.
+
+    * For **real** (materialized) slots: ``id`` is set, ``virtual_id`` is None.
+    * For **virtual** (plan-generated) slots: ``id`` is None, ``virtual_id``
+      is the ``plan-{plan_id}-{date}`` identifier.
+    """
+    id: Optional[int] = Field(None, description="Real slot DB id (None for virtual)")
+    virtual_id: Optional[str] = Field(None, description="Virtual slot id (None for real)")
+    user_id: int
+    date: date
+    slot_type: str
+    estimated_duration: int
+    scheduled_at: str  # HH:MM:SS ISO format
+    started_at: Optional[str] = None
+    attended: bool
+    actual_duration: Optional[int] = None
+    event_type: Optional[str] = None
+    event_data: Optional[dict[str, Any]] = None
+    priority: int
+    status: str
+    plan_id: Optional[int] = None
+    created_at: Optional[datetime] = None
+    updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class CalendarDayResponse(BaseModel):
+    """Response for a single-day calendar query."""
+    date: date
+    user_id: int
+    slots: list[CalendarSlotItem] = Field(
+        default_factory=list,
+        description="All slots for the day, sorted by scheduled_at ascending",
+    )