fix(server): serialize Postgres-backed test files to stop real deadlocks

The postgres-*.test.ts suites all run against one shared Postgres
instance (CI's real service container). vitest's default file-level
parallelism runs these files concurrently across worker processes,
which is exactly what produced the deadlocks (AccessExclusiveLock/
RowShareLock contention) and foreign-key violations the first real
Postgres-backed CI run just surfaced -- these suites never ran against
real Postgres in CI before today. Set fileParallelism: false so they
serialize instead; correctness over wall-clock time is the right trade
for integration tests against genuinely shared, unpartitioned state.

Not independently verifiable here (no local Postgres/Redis in this
environment) -- the non-Postgres suite (647 tests) still passes
unchanged with this config.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: voidstackloop

server/vitest.config.ts

@@ -4,5 +4,21 @@ export default defineConfig({
     test: {
         environment: "node",
         include: ["src/**/*.test.ts"],
+        // The postgres-*.test.ts suites (see e.g. postgres-rls.test.ts's own
+        // disclosure comment) all run against ONE real shared Postgres
+        // instance (CI's DATABASE_URL service container; a developer's own
+        // local instance otherwise) — vitest's default file-level
+        // parallelism runs these files concurrently across worker
+        // processes, and real, unrelated-looking Postgres deadlocks
+        // (AccessExclusiveLock/RowShareLock contention) and foreign-key
+        // violations (one file's teardown removing a row another file's
+        // in-flight test still references) are the direct result, first
+        // surfaced when this package's Postgres suites started actually
+        // running in CI (see the "server" job's own comment in
+        // .github/workflows/ci.yml). Serializing files here trades some
+        // wall-clock time for correctness against genuinely shared,
+        // unpartitioned state — the correct trade for integration tests,
+        // not a workaround for a test bug.
+        fileParallelism: false,
     },
 });