M0: foundation — monorepo, PostGIS schema, deck query, app shell

Greenfield scaffold for Linkder, a swipe-to-hire marketplace for local
professional services.

- pnpm/turbo monorepo: apps/web, packages/{shared,db}
- Postgres 16 + PostGIS via docker compose (ports 5442/6389 to avoid
  clashing with other local stacks)
- Drizzle schema, 23 tables, geography(Point,4326) with GiST indexes
- Domain core in packages/shared: integer-cent money, status transition
  graphs, deck ranking weights, cancellation policy — 46 unit tests
- Deck query: filtering in Postgres on the GiST index, ranking in JS so
  the weights stay tunable — 18 integration tests against a seeded DB
- Deterministic seed placing pros at known distances, including three
  that must NOT appear on a deck (out of radius, unverified, away)
- Next.js 15 app shell with a working swipe deck
- CI: typecheck, lint, test, build against live postgres+redis

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

.github/workflows/ci.yml

@@ -0,0 +1,60 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+
+    services:
+      postgres:
+        image: postgis/postgis:16-3.4
+        env:
+          POSTGRES_USER: linkder
+          POSTGRES_PASSWORD: linkder
+          POSTGRES_DB: linkder
+        ports: ['5442:5432']
+        options: >-
+          --health-cmd "pg_isready -U linkder -d linkder"
+          --health-interval 5s --health-timeout 5s --health-retries 10
+      redis:
+        image: redis:7-alpine
+        ports: ['6389:6379']
+        options: >-
+          --health-cmd "redis-cli ping"
+          --health-interval 5s --health-timeout 3s --health-retries 10
+
+    env:
+      DATABASE_URL: postgresql://linkder:linkder@localhost:5442/linkder
+      REDIS_URL: redis://localhost:6389
+      NEXT_PUBLIC_CITY_LAT: '41.3874'
+      NEXT_PUBLIC_CITY_LNG: '2.1686'
+      NEXT_PUBLIC_CITY_NAME: Barcelona
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+
+      - run: pnpm install --frozen-lockfile
+
+      # The integration tests assert against exact seeded distances, so the
+      # database must be migrated and seeded before they run.
+      - run: cp .env.example .env
+      - run: pnpm db:migrate
+      - run: pnpm db:seed
+
+      - run: pnpm typecheck
+      - run: pnpm lint
+      - run: pnpm test
+      - run: pnpm build