add nix development environment

Provide a direnv-loaded Laravel and future Vue toolchain with isolated worktree ports and a process-compose stack. Use PostgreSQL for local runtime services while retaining in-memory SQLite for PHPUnit.

process-compose.yaml

@@ -0,0 +1,59 @@
+version: "0.5"
+
+processes:
+  postgres:
+    command: postgres -D "$PGDATA" -k "$PGDATA" -c listen_addresses=''
+    shutdown:
+      signal: 2
+    readiness_probe:
+      exec:
+        command: pg_isready -h "$PGDATA" -d "$PGDATABASE" -U "$PGUSER"
+      initial_delay_seconds: 1
+      period_seconds: 2
+
+  migrate:
+    command: php artisan migrate --force
+    working_dir: ./backend
+    depends_on:
+      postgres:
+        condition: process_healthy
+
+  mailpit:
+    command: mailpit --smtp 127.0.0.1:${MAILPIT_SMTP_PORT:-2525} --listen 127.0.0.1:${MAILPIT_UI_PORT:-8025}
+    readiness_probe:
+      http_get:
+        host: 127.0.0.1
+        port: ${MAILPIT_UI_PORT:-8025}
+        path: /
+      initial_delay_seconds: 1
+      period_seconds: 2
+
+  backend:
+    command: php artisan serve --host=127.0.0.1 --port=${BACKEND_PORT:-8001}
+    working_dir: ./backend
+    depends_on:
+      migrate:
+        condition: process_completed_successfully
+      mailpit:
+        condition: process_healthy
+    readiness_probe:
+      http_get:
+        host: 127.0.0.1
+        port: ${BACKEND_PORT:-8001}
+        path: /up
+      initial_delay_seconds: 2
+      period_seconds: 10
+
+  caddy:
+    command: caddy run --config Caddyfile --adapter caddyfile
+    depends_on:
+      backend:
+        condition: process_healthy
+    readiness_probe:
+      http_get:
+        host: 127.0.0.1
+        port: ${CADDY_PORT:-8000}
+        path: /up
+        scheme: https
+      initial_delay_seconds: 1
+      period_seconds: 2