review fixes: seeded-auth hard gate, ci.yml build serialization, assets 404

- M1: E2E_REQUIRE_SEEDED_AUTH=1 in the CI e2e step makes login failures hard
  failures (loginAs throws, guards disabled, globalSetup refuses a pre-populated
  DB); auth.spec redirect test asserts outright under the flag; non-admin
  /admin test is now a real authorization assertion
- M2: ci.yml build step depends_on test — never two concurrent turbo builds
  on the shared workspace
- M3: unknown /assets/* paths 404 from the SPA catch-all instead of serving
  index.html with an immutable cache header; spec arm added
- minors: e2e step gets when: *image_build_when, health poll uses
  GATEWAY_PORT + AbortSignal.timeout, BETTER_AUTH_SECRET generated per run
  (no literal in tree), failure echoes artifact path, dev-guide documents the
  gate, stale verify-release comment fixed

scripts/verify-release.mjs

@@ -106,8 +106,8 @@ export const STAGES = [
   {
     // RI-N4 (QC-19, card RI-3-002): the typed quality-rails evaluator, invoked
     // as the implementation of the check it owns instead of a duplicated
-    // presence loop here. Canonical-only stage (no ci.yml mirror — same shape
-    // as `build`); runs AFTER build so the evaluator's dist/ exists. Subject
+    // presence loop here. Canonical-only stage (no ci.yml mirror; `build`
+    // gained one in #1445); runs AFTER build so the evaluator's dist/ exists. Subject
     // is this repository (`.` → monorepo subject kind, per-subject check set).
     name: 'quality-rails',
     commands: ['node packages/quality-rails/dist/cli.js quality-rails evaluate --project .'],