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)

README.md

@@ -18,6 +18,7 @@ Nail salon booking platform — Go 1.25 backend + SvelteKit 5 frontend + Docker.
 - **CardDAV sync**: profile photos synced to SabreDAV contacts
 - **Admin notifications**: priority-sorted queue with bell icon, `/notifications` page, acknowledge flow
 - **User notification preferences**: per-channel toggles (email, SMS, browser) in account settings
+- **Enriched edit requests**: side-by-side original vs proposed booking snapshots (time, services, prices, durations, user details) for admin review
 
 ## Project Structure
 
@@ -89,7 +90,7 @@ cd backend && go build -o bin/backend ./main.go
 # Frontend
 cd frontend && npm ci && npm run build
 
-# Tests (396/399 passing, 3 skipped)
+# Tests (438/441 passing, 3 skipped)
 cd backend && go test -tags "test,dev" ./...
 ```