Add timezone selector to Admin settings with full-stack support

- Add `timezone` column to User model (VARCHAR 64, default UTC) with
  idempotent startup migration
- Expose and persist timezone via PATCH /api/users/me
- Fix TimerEvent.occurred_at serialization to include UTC offset marker
  (+00:00) so JavaScript correctly parses timestamps as UTC
- Add frontend utility (src/utils/time.js) with timezone-aware
  formatTime, getHHMM, getDateInTZ, tzDateTimeToUTC helpers and a
  curated IANA timezone list
- Add Settings section to Admin page with timezone dropdown; saves to
  both the API and localStorage for the unauthenticated TV view
- Update Activity Log to display and edit times in the user's timezone
- Update TV dashboard clock to respect the saved timezone
- Update README: features, setup steps, usage table, WebSocket events

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -33,6 +33,7 @@ async def lifespan(app: FastAPI):
         await _add_column_if_missing(conn, "schedule_templates", "day_end_time", "TIME NULL")
         await _add_column_if_missing(conn, "schedule_blocks", "duration_minutes", "INT NULL")
         await _add_column_if_missing(conn, "children", "strikes", "INT NOT NULL DEFAULT 0")
+        await _add_column_if_missing(conn, "users", "timezone", "VARCHAR(64) NOT NULL DEFAULT 'UTC'")
     yield
 
 

backend/app/models/user.py

@@ -12,6 +12,7 @@ class User(TimestampMixin, Base):
     full_name: Mapped[str] = mapped_column(String(255), nullable=False)
     is_active: Mapped[bool] = mapped_column(Boolean, default=True)
     is_admin: Mapped[bool] = mapped_column(Boolean, default=False)
+    timezone: Mapped[str] = mapped_column(String(64), nullable=False, default="UTC")
 
     children: Mapped[list["Child"]] = relationship("Child", back_populates="user")  # noqa: F821
     subjects: Mapped[list["Subject"]] = relationship("Subject", back_populates="user")  # noqa: F821

backend/app/routers/users.py

@@ -23,6 +23,8 @@ async def update_me(
         current_user.full_name = body.full_name
     if body.email is not None:
         current_user.email = body.email
+    if body.timezone is not None:
+        current_user.timezone = body.timezone
     await db.commit()
     await db.refresh(current_user)
     return current_user

backend/app/schemas/activity.py

@@ -1,5 +1,5 @@
-from datetime import date, datetime
-from pydantic import BaseModel
+from datetime import date, datetime, timezone
+from pydantic import BaseModel, field_serializer
 
 
 class ActivityLogCreate(BaseModel):
@@ -45,3 +45,9 @@ class TimelineEventOut(BaseModel):
     subject_name: str | None = None
     subject_icon: str | None = None
     subject_color: str | None = None
+
+    @field_serializer("occurred_at")
+    def serialize_occurred_at(self, dt: datetime) -> str:
+        if dt.tzinfo is None:
+            dt = dt.replace(tzinfo=timezone.utc)
+        return dt.isoformat()

backend/app/schemas/user.py

@@ -7,6 +7,7 @@ class UserOut(BaseModel):
     full_name: str
     is_active: bool
     is_admin: bool
+    timezone: str = "UTC"
 
     model_config = {"from_attributes": True}
 
@@ -14,3 +15,4 @@ class UserOut(BaseModel):
 class UserUpdate(BaseModel):
     full_name: str | None = None
     email: EmailStr | None = None
+    timezone: str | None = None