fix(test): serialize packages (-p 1) to stop embedded-postgres data-dir race

CI check failed in internal/adapters/store: parallel 'go test ./...' starts
multiple embedded-postgres instances against the shared ~/.embedded-postgres-go
data dir → 'another postgres running in data directory'. -p 1 runs one package
at a time, so only one embedded-postgres is live. (Locally flaky, deterministic
in CI's fresh env.)

Taskfile.yml

@@ -37,9 +37,10 @@ tasks:
       - 'command -v golangci-lint >/dev/null 2>&1 && golangci-lint run ./... || echo "golangci-lint not installed — skipping (CI installs it)"'
 
   test:
-    desc: Run all tests, including the acceptance suite (RED until the engine is implemented).
+    desc: Run all tests. -p 1 serializes packages so the embedded-postgres tests
+      (store, web, oidc) don't race on the shared ~/.embedded-postgres-go data dir.
     cmds:
-      - go test ./...
+      - go test -p 1 ./...
 
   generate:
     desc: Regenerate Templ components (*_templ.go) from *.templ sources.