feat: enriched edit request system with side-by-side snapshots, calendar preloading, and admin review UI

Backend:
- Add enriched response types (EditSnapshot, EnrichedEditRequest) with original vs proposed snapshots
- Add 4 new GET endpoints for viewing edit requests (user and admin scoped)
- Remove github.com/lib/pq dependency — use native PostgreSQL array scanning
- Clean up edit requests, time blockers, and notifications on booking cancellation
- Validate exceptional closed hours on admin approve (409 Conflict)
- Notification upsert on edit request replace (no duplicate admin notifications)

Frontend:
- New user EditRequestModal with time/services/both modes and lunch protection
- New admin EditRequestModal with side-by-side diff (date/time, services, notes)
- Integrate edit requests into PendingApprovals card and notifications page
- Preload 3 months of availability to prevent calendar snap-back
- Apply lunch protection to isDateUnavailable in BookingFlow and BookingCreateModal
- Fix accessibility: card list items use <button> instead of <div>

Dev & Docs:
- Seed edit requests in local-dev-2.sh
- Update all Obsidian manuals with enriched edit request documentation
- 42 new tests (438/441 passing)

backend/handlers/admin/bookings_test.go

@@ -35,7 +35,6 @@ import (
 	"crussell/testutils/fixtures"
 
 	"github.com/go-chi/chi/v5"
-	"github.com/lib/pq"
 )
 
 // =============================================================================
@@ -1511,7 +1510,7 @@ func TestAdminBookings_ListEditRequests(t *testing.T) {
 			INSERT INTO booking_edit_requests (booking_id, requested_by, new_start_time, new_services, notes, has_overrides)
 			VALUES ($1, $2, $3, $4, $5, $6)`,
 			bookingID, userID, time.Now().Add(time.Duration(i)*24*time.Hour),
-			pq.Array(&emptyServices), fmt.Sprintf("Edit request %d", i), false)
+			emptyServices, fmt.Sprintf("Edit request %d", i), false)
 		if err != nil {
 			t.Fatalf("failed to create edit request %d: %v", i, err)
 		}
@@ -1714,7 +1713,7 @@ func TestAdminBookings_ApproveEditRequest(t *testing.T) {
 		`INSERT INTO booking_edit_requests (booking_id, requested_by, new_start_time, new_services, notes)
 		VALUES ($1, $2, $3, $4, 'Please change time')
 		RETURNING id`,
-		bookingID, userID, newStartTime, pq.Array(&emptyServices)).Scan(&editRequestID)
+		bookingID, userID, newStartTime, emptyServices).Scan(&editRequestID)
 	if err != nil {
 		t.Fatalf("failed to create edit request: %v", err)
 	}