feat(api): add unified v2 gateway and mobile read slice

docs/BACKEND/API_GUIDES/V2/mobile-api-gap-analysis.md

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+# Mobile API Gap Analysis
+
+Source compared against implementation:
+
+- `/Users/wiel/Downloads/mobile-backend-api-specification.md`
+
+## Implemented in this slice
+
+- unified frontend-facing base URL design
+- client auth wrapper for email/password sign-in and sign-up
+- auth session and sign-out endpoints
+- client read surface for dashboard, billing, coverage, hubs, vendor lookup, and date-range order items
+- staff read surface for dashboard, availability, clock-in reads, payments, shifts, and profile sections
+- schema support for:
+  - cost centers
+  - hub managers
+  - recurring staff availability
+  - staff benefits
+- seed support for:
+  - authenticated demo staff user
+  - cost center and hub manager data
+  - staff benefits and availability
+  - attire and tax-form example documents
+
+## Still missing
+
+### Auth
+
+- staff phone OTP start
+- staff OTP verify
+- staff profile setup endpoint
+
+### Client writes
+
+- hub create
+- hub update
+- hub delete
+- hub NFC assignment
+- assign manager to hub
+- invoice approve
+- invoice dispute
+
+### Staff writes
+
+- availability update
+- availability quick set
+- shift apply
+- shift decline
+- request swap
+- personal info update
+- preferred locations update
+- profile photo upload wrapper
+
+### Reports
+
+- report summary
+- daily ops
+- spend
+- coverage
+- forecast
+- performance
+- no-show
+
+### Core persistence
+
+- `core-api-v2` verification jobs still need durable SQL persistence