feat: agent-11 PR1 – Vertretung, Storno-Re-Genehmigung, Kommentare

Abwesenheits-Modul abgerundet (Feature-Parität mit Urlaubsverwaltung):

- Vertretung: Overlap-Warnung beim Anlegen, E-Mail an Vertretung bei
  Genehmigung, GET /absences/?as_substitute=true, neuer schlanker
  GET /users/colleagues (alle Rollen, RLS-gefenced) für die Auswahl;
  Vertreter-Dropdown + Anzeige in der Liste.
- Stornierung mit Re-Genehmigung: neuer Status CANCELLATION_REQUESTED,
  POST /absences/{id}/request-cancellation; Manager genehmigt/lehnt über
  bestehende approve/reject ab (Urlaub + FZA-Rückbuchung via _apply_cancellation).
- Kommentare: Model AbsenceComment (company_id-RLS), GET/POST comments,
  System-Kommentare bei Statuswechsel, AbsenceCommentsModal.
- Fix: CalDAV fire-and-forget nutzte die Request-Session weiter (in Tests
  geteilt -> "another operation in progress"); jetzt sync_*_bg mit eigener
  Session + RLS-Bypass.

Migration 0035. 178/178 Tests grün. Deployed auf 137 + 164.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -8,6 +8,7 @@ from app.models.work_schedule import WorkSchedule
 from app.models.time_entry import TimeEntry, EntryStatus, EntrySource
 from app.models.absence_type import AbsenceType
 from app.models.absence import Absence, AbsenceStatus
+from app.models.absence_comment import AbsenceComment
 from app.models.vacation_balance import VacationBalance
 from app.models.overtime_balance import OvertimeBalance
 from app.models.public_holiday import PublicHoliday
@@ -32,6 +33,7 @@ __all__ = [
     "AbsenceType",
     "Absence",
     "AbsenceStatus",
+    "AbsenceComment",
     "VacationBalance",
     "OvertimeBalance",
     "PublicHoliday",

backend/app/models/absence.py

@@ -16,10 +16,13 @@ if TYPE_CHECKING:
 
 
 class AbsenceStatus(str, enum.Enum):
-    PENDING   = "pending"
-    APPROVED  = "approved"
-    REJECTED  = "rejected"
-    CANCELLED = "cancelled"
+    PENDING                = "pending"
+    APPROVED               = "approved"
+    REJECTED               = "rejected"
+    CANCELLED              = "cancelled"
+    # Mitarbeiter hat für einen bereits genehmigten Antrag eine Stornierung
+    # beantragt – Manager muss zustimmen (→ cancelled) oder ablehnen (→ approved).
+    CANCELLATION_REQUESTED = "cancellation_requested"
 
 
 class Absence(Base):

backend/app/models/absence_comment.py

@@ -0,0 +1,44 @@
+import uuid
+from datetime import datetime
+from typing import TYPE_CHECKING
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, Text, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.core.database import Base
+
+if TYPE_CHECKING:
+    from app.models.user import User
+
+
+class AbsenceComment(Base):
+    """Kommentar-Thread an einem Abwesenheitsantrag.
+
+    `company_id` wird redundant gespeichert, damit die Tabelle über die normale
+    company_id-RLS-Policy gefenced werden kann (kein Join nötig). System-Kommentare
+    (`is_system=True`) werden bei Statuswechseln automatisch erzeugt.
+    """
+    __tablename__ = "absence_comments"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    absence_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("absences.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    company_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("companies.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    author_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL")
+    )
+    body: Mapped[str] = mapped_column(Text, nullable=False)
+    is_system: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+    author: Mapped["User | None"] = relationship(
+        "User", primaryjoin="AbsenceComment.author_id == User.id",
+        foreign_keys="[AbsenceComment.author_id]", lazy="noload",
+    )
+
+    def __repr__(self) -> str:
+        return f"<AbsenceComment {self.absence_id} by {self.author_id}>"