fix: panic recovery, rate limiting, transaction error handling, pagination

Hardening pass over the API surface. No route's auth requirements change.

Resilience:
- Add recover middleware. There was none, so an unhandled panic in any
  handler propagated out of the process instead of becoming a 500.
- Add a centralized ErrorHandler so errors and recovered panics return the
  same {success,message} envelope as the utils helpers, not Fiber's default
  plain-text body. 5xx responses are logged with method and path.

Rate limiting:
- Global 300/min per IP as an abuse backstop, exempting health/readiness
  probes and websocket upgrades.
- 10/min shared across every credential endpoint (customer/miler/admin/hub
  login, verify-pin, reset-pin, email OTP). PINs are 4 digits, so the whole
  keyspace was previously walkable in seconds. One shared limiter instance
  means rotating between endpoints doesn't reset the budget.
- Add TRUSTED_PROXIES config. Limits key on c.IP(), which behind a TLS
  terminator is the proxy, collapsing every client into one bucket. When set,
  X-Forwarded-For is honoured only from those proxies so the header can't be
  spoofed to dodge the limit. Logs a warning when unset.

Transactions:
- Check the error on all 51 previously-unchecked tx.Save/Create/Delete/
  Model(...).Update/Commit calls across 6 controllers. A failed write inside
  a transaction was silently ignored and the request still reported success;
  an unchecked Commit could fail with the caller told everything worked.
  Each site now rolls back and returns a specific message.

Pagination:
- Add utils.ParsePage/Paginated, reusing the pageno/pagesize convention
  GetAdminBookings already established. Default 500, hard cap 1000.
- Apply to the previously unbounded consignments, tripsheets, exceptions,
  app-users and clients endpoints. Defaults are high so existing consoles
  that don't paginate keep working; the cap only stops a growing table from
  being loaded wholesale. total is now a real COUNT, not len(data).
- GetClients also loaded the entire auth table to join in memory; it now
  fetches only the current page's rows.

Tests (first in the repo):
- Extract the hyperlocal pincode rule out of BookingPickupComplete into
  isHyperlocal so it is testable, covering the short/empty pincode fallback.
- Cover calculateVolumetricWeight and the ParsePage clamping rules.

Repo hygiene:
- Tag scratch/*.go with //go:build ignore. Each declared its own main(), so
  `go build ./...` failed on redeclaration; it now passes repo-wide.
- Untrack scratch/node_modules (216 files) and ignore node_modules, test
  artifacts, and the `doormile` binary `go build .` emits.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.env.example

@@ -4,6 +4,13 @@ ENV=development
 JWT_SECRET_KEY=DoormileSuperSecretJWTKey2026!
 INTERNAL_API_KEY=doormile-internal-2024
 
+# Reverse proxy — comma-separated IPs/CIDRs allowed to set X-Forwarded-For.
+# Rate limiting keys on the client IP, so if this service sits behind nginx or
+# any TLS terminator this MUST list that proxy; otherwise every request looks
+# like it came from the proxy and all clients share one rate-limit bucket.
+# Leave empty only when the app is exposed directly.
+# TRUSTED_PROXIES=127.0.0.1,10.0.0.0/8
+
 # PostgreSQL Database Configuration
 DB_HOST=31.97.228.132
 DB_PORT=5433