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

.woodpecker/ci.yml

@@ -264,7 +264,12 @@ steps:
       - *enable_pnpm
       - pnpm build
     depends_on:
-      - typecheck
+      # after test, not typecheck: turbo gives `test` a ^build dependency, so
+      # running this step concurrently with test would put two independent
+      # turbo builds on the same shared-workspace dist/ and turbo cache with
+      # no cross-process locking — the same serialization invariant
+      # publish.yml documents for #1411.
+      - test
 
 services:
   ci-postgres: