feat: backdated reported date for old active tickets

Wahab can now enter historical tickets that keep their true reported date:

- Add nullable tickets.reported_at (DateTime) via alembic d5e0f2a1c3b4;
  backfill existing rows from created_at so nothing shows empty.
- TicketCreate.reported_at (optional) is persisted by create_ticket and
  defaults to now when omitted, so existing create behavior is unchanged.
- New-issue form gains a 'Reported Date' date picker (defaults to today,
  past dates allowed, future blocked) and sends reported_at in the payload.
- List and detail pages show 'Reported' next to 'Created' (date-only,
  labeled) so backdated tickets are obvious; SLA deadline is unchanged and
  still runs from creation time so backfilling never instantly breaches.
- Tests: backdated create persists + is exposed on list/detail; omitted
  reported_at defaults to now; SLA window unchanged; full datetime round trip.

app/services/ticket.py

@@ -114,6 +114,10 @@ async def create_ticket(
     ticket_number = await _generate_ticket_number(db)
     priority = data.get("priority")
     sla_deadline = compute_sla_deadline(priority) if priority else None
+    # Original report date: backdated/backfilled tickets keep their true date;
+    # when omitted the ticket is considered reported right now. The SLA clock
+    # is unchanged — deadlines run from creation time, not the reported date.
+    reported_at = data.get("reported_at") or datetime.now(timezone.utc)
 
     ticket = Ticket(
         ticket_number=ticket_number,
@@ -126,6 +130,7 @@ async def create_ticket(
         reported_via=data.get("reported_via"),
         description=data.get("description"),
         assigned_to=data.get("assigned_to"),
+        reported_at=reported_at,
         sla_deadline=sla_deadline,
     )
     db.add(ticket)