fix: rate-limit per-IP keying + dev no-op, admin 2FA recovery, 2FA account UI, admin modals, tip totals

Rate limiting (backend):
- RateLimit/ProgressiveRateLimit now derive the per-client key from
  CF-Connecting-IP, then chi's GetClientIP (the X-Real-IP value nginx sets at
  main.go:323), then RemoteAddr. Previously only CF-Connecting-IP/RemoteAddr
  were used, so behind the Docker nginx every client shared ONE bucket per
  limiter — 10 logins/min site-wide blocked all users (the reported
  'Error: Rate limit exceeded' after seeding was the login 10/min bucket
  tripped by the seed's 11 logins, all keyed 127.0.0.1 in dev).
- Real implementation is now //go:build !dev || test; new
  mw/ratelimit_dev.go (//go:build dev && !test) is a no-op passthrough, so
  'go run -tags dev' (the dev harness) never rate-limits dev/seeding traffic,
  while production and tests (-tags test,dev) keep the real limiter. The docs
  (Technical Manual) already claimed dev no-op behaviour — the code now
  matches. NewProgressiveRateLimiter is provided in the no-op build because
  tag-free ratelimit_shared.go:104 initializes the global at package init.

Admin 2FA management (backend):
- users.two_factor_last_used_at TIMESTAMPTZ column (init-script, fresh-DB).
- AdminUserDetail now returns twoFactorEnabled/twoFactorMethod/
  twoFactorLastUsedAt.
- New POST /api/admin/users/{id}/2fa/remove (admin-only): clears all 5 2FA
  columns + drops the user's in-memory attempt/lockout state — an admin
  recovery path when a user loses 2FA access.
- two_factor_last_used_at updated on every successful 2FA verification.

Account page (/account):
- 2FA section moved under the Notifications heading, visible to all roles;
  Email/SMS toggles (Notifications styling) acting as a radio group with
  'none' state; Apply button only when the selection differs from saved;
  unselecting shows a payment-rules warning dialog; the dev-comment
  '2FA is optional right now (REQUIRE_2FA is off)' and the 'Dev code:' debug
  line are removed.
- Cards tab hidden from admin role.

Admin modals:
- User Details modal: new 'Two-Factor Authentication' section above Patch
  Tests showing Enabled/Disabled, method, last-used timestamp, and a Remove
  2FA button with a confirmation dialog (POST to the admin endpoint, refetch
  on success).
- Booking Details modal: the customer's name now links to their User Details
  modal (optional openUserModal prop threaded through admin/+page and
  today/+page; other call sites unaffected).

Take Payment + /today:
- PaymentModal shows pre-tip (netTotal) and post-tip (totalWithTip) totals
  with a tip-amount delta row only when a tip is selected; zero-tip flow
  unchanged.
- The /today Payment button is hidden unless the booking is in_progress or
  completed, matching the backend gate (was shown for confirmed/pending
  bookings, producing the 'Booking must be in_progress or completed' error).

Verification: go test -tags test,dev -count=1 -parallel 8 ./... (20/20 ok
incl. new admin 2FA tests + mw tests), go build ./... and -tags dev both
compile, go vet clean, svelte-check 0 errors 0 warnings, env-docs gate OK,
docker compose config valid.

backend/mw/ratelimit_dev.go

@@ -0,0 +1,36 @@
+//go:build dev && !test
+
+// No-op rate limiting for pure dev builds (-tags dev): the dev seed performs
+// more logins/requests than the real limiters allow in a minute, which would
+// block local development. Tests always build with the `test` tag, so the real
+// implementation in ratelimit.go is used there. The types, registration, and
+// Cleanup methods come from tag-free ratelimit_shared.go.
+
+package mw
+
+import (
+	"net/http"
+	"time"
+)
+
+func NewRateLimiter(limit int, window time.Duration) *RateLimiter {
+	return &RateLimiter{}
+}
+
+func NewProgressiveRateLimiter() *ProgressiveRateLimiter {
+	return &ProgressiveRateLimiter{}
+}
+
+func ProgressiveRateLimit(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		next.ServeHTTP(w, r)
+	})
+}
+
+func RateLimit(limit int, window time.Duration) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			next.ServeHTTP(w, r)
+		})
+	}
+}