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/bookings/bookings_test.go

@@ -36,7 +36,6 @@ import (
 
 	"github.com/go-chi/chi/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
-	"github.com/lib/pq"
 )
 
 func resetTestData(t *testing.T) {
@@ -2860,7 +2859,7 @@ func TestAdminApproveEditRequest(t *testing.T) {
 		t.Fatalf("failed to confirm booking: %v", err)
 	}
 
-	// Create edit request directly in DB (need pq.Array for PostgreSQL array)
+	// Create edit request directly in DB
 	var editRequestID string
 	newTime := time.Now().Add(24 * time.Hour).Truncate(time.Minute)
 	var emptyServices []string
@@ -2868,7 +2867,7 @@ func TestAdminApproveEditRequest(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, newTime, pq.Array(&emptyServices)).Scan(&editRequestID)
+		bookingID, userID, newTime, emptyServices).Scan(&editRequestID)
 	if err != nil {
 		t.Fatalf("failed to create edit request: %v", err)
 	}