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)

frontend/src/lib/components/payments/UserPaymentModal.svelte

@@ -471,8 +471,9 @@
 							{#if showCardList}
 								<div class="space-y-2">
 									{#if canSaveCards}
-										<div
-											class="flex items-center justify-between rounded-lg border p-3 cursor-pointer hover:border-gray-300 transition-colors"
+										<button
+											type="button"
+											class="flex w-full items-center justify-between rounded-lg border p-3 hover:border-gray-300 transition-colors"
 											onclick={() => {
 												showNewCardForm = true;
 												showCardList = false;
@@ -483,11 +484,12 @@
 											<svg class="h-4 w-4 text-gray-400" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
 												<path d="M9 18l6-6-6-6" />
 											</svg>
-										</div>
+										</button>
 									{/if}
 									{#each paymentMethods as method (method.id)}
-										<div
-											class="flex items-center justify-between rounded-lg border p-3 cursor-pointer {selectedPaymentMethod === method.id ? 'border-input bg-fuchsia-100' : 'border-input hover:bg-fuchsia-50'}"
+										<button
+											type="button"
+											class="flex w-full items-center justify-between rounded-lg border p-3 {selectedPaymentMethod === method.id ? 'border-input bg-fuchsia-100' : 'border-input hover:bg-fuchsia-50'}"
 											onclick={() => {
 												selectedPaymentMethod = method.id;
 												showNewCardForm = false;
@@ -508,7 +510,7 @@
 											{#if selectedPaymentMethod === method.id}
 												<span class="text-xs font-medium text-foreground">Selected</span>
 											{/if}
-										</div>
+										</button>
 									{/each}
 								</div>
 							{/if}