fix(demo): anchor seeded dates to the real reset moment

Booking/inspection/maintenance/outbox dates were authored as absolute
timestamps around a fixed 2026-08-01 anchor and never re-anchored at
seed/reset time, so demo scenarios (e.g. BK-DEMO-RETURN) silently drifted
into the past. Every reset now shifts seeded dates by (today - authored
anchor); dashboard's "today" filter uses real wall-clock time instead of
the now-removed frozen demo_today setting. Adds seed-validation tests
proving scenarios S1/S2/S4/S5 are present and internally consistent after
every reset.

backend/app/seed_loader.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 import csv
 import uuid
 from dataclasses import dataclass
-from datetime import UTC, datetime
+from datetime import UTC, date, datetime, timedelta
 from pathlib import Path
 
 from sqlalchemy import delete, insert, update
@@ -20,6 +20,7 @@ from app.models.maintenance import MaintenanceRecord
 from app.models.outbox import OutboxEvent
 from app.models.user import User
 from app.models.vehicle import Vehicle
+from app.services.audit import record_audit_event
 
 settings = get_settings()
 
@@ -36,6 +37,17 @@ DEMO_USERS = [
     },
 ]
 
+# seed/generate_seed.py authored the committed CSVs relative to this fixed date
+# (`--anchor 2026-08-01`, matching Settings.demo_today). Every reset shifts every
+# seeded date by (today - SEED_AUTHORED_ANCHOR) so "today" / "near-future" / "overlaps
+# right now" scenarios stay true to the actual reset moment instead of decaying as real
+# time passes between resets -- a fixed anchor with no shift goes stale within days.
+SEED_AUTHORED_ANCHOR = date(2026, 8, 1)
+
+
+def _seed_anchor_shift(today: date) -> timedelta:
+    return today - SEED_AUTHORED_ANCHOR
+
 
 def _parse_dt(value: str) -> datetime:
     return datetime.fromisoformat(value.replace("Z", "+00:00"))
@@ -53,6 +65,8 @@ def _parse_optional_int(value: str) -> int | None:
 @dataclass
 class SeedResult:
     counts: dict[str, int]
+    anchor_date: date
+    seeded_at: datetime
 
 
 def _seed_dir() -> Path:
@@ -83,6 +97,8 @@ def clear_all(db: Session) -> None:
 
 def load_seed(db: Session) -> SeedResult:
     counts: dict[str, int] = {}
+    today = datetime.now(UTC).date()
+    shift = _seed_anchor_shift(today)
 
     user_rows = [
         {"id": uuid.uuid4(), **user, "active": True} for user in DEMO_USERS
@@ -154,8 +170,8 @@ def load_seed(db: Session) -> SeedResult:
                 "public_ref": row["public_ref"],
                 "customer_id": customer_id_by_ref[row["customer_ref"]],
                 "vehicle_id": vehicle_id_by_ref[row["vehicle_ref"]],
-                "starts_at": _parse_dt(row["starts_at"]),
-                "ends_at": _parse_dt(row["ends_at"]),
+                "starts_at": _parse_dt(row["starts_at"]) + shift,
+                "ends_at": _parse_dt(row["ends_at"]) + shift,
                 "status": row["status"],
                 "start_odometer_km": _parse_optional_int(row["start_odometer_km"]),
                 "end_odometer_km": _parse_optional_int(row["end_odometer_km"]),
@@ -179,7 +195,7 @@ def load_seed(db: Session) -> SeedResult:
                 "damage_reported": _parse_bool(row["damage_reported"]),
                 "technical_warning": _parse_bool(row["technical_warning"]),
                 "odometer_km": int(row["odometer_km"]),
-                "completed_at": _parse_dt(row["completed_at"]),
+                "completed_at": _parse_dt(row["completed_at"]) + shift,
                 "completed_by": None,
             }
         )
@@ -193,7 +209,7 @@ def load_seed(db: Session) -> SeedResult:
                 "id": uuid.uuid4(),
                 "public_ref": row["public_ref"],
                 "vehicle_id": vehicle_id_by_ref[row["vehicle_ref"]],
-                "occurred_at": _parse_dt(row["occurred_at"]),
+                "occurred_at": _parse_dt(row["occurred_at"]) + shift,
                 "odometer_km": int(row["odometer_km"]),
                 "category": row["category"],
                 "summary": row["summary"],
@@ -266,7 +282,7 @@ def load_seed(db: Session) -> SeedResult:
                     },
                     "aggregate_ref": row["aggregate_ref"],
                 },
-                "occurred_at": _parse_dt(row["occurred_at"]),
+                "occurred_at": _parse_dt(row["occurred_at"]) + shift,
                 "delivery_status": row["status"],
                 "attempts": int(row["attempts"]),
                 "next_attempt_at": None,
@@ -277,7 +293,21 @@ def load_seed(db: Session) -> SeedResult:
     db.execute(insert(OutboxEvent), outbox_rows)
     counts["workflow_runs"] = len(outbox_rows)
 
-    return SeedResult(counts=counts)
+    seeded_at = datetime.now(UTC)
+    record_audit_event(
+        db,
+        actor_type="system",
+        actor_label="seed loader",
+        action="demo_data_seeded",
+        entity_type="system",
+        metadata={
+            "anchor_date": today.isoformat(),
+            "seed_authored_anchor": SEED_AUTHORED_ANCHOR.isoformat(),
+            "counts": counts,
+        },
+    )
+
+    return SeedResult(counts=counts, anchor_date=today, seeded_at=seeded_at)
 
 
 def reset_and_seed(db: Session) -> SeedResult: