Phase 008: close the test and CI loop around the migration

Adds the checks that make the constraints from Phase 001-007 mechanical
instead of tribal knowledge, and clears the legacy brand text that was still
reachable at runtime.

New red-line tests:
  - no-legacy-brand mirrors the harness scan under vitest, and asserts its
    allow-list has not drifted from harness-check.mjs
  - hermes-db-readonly classifies every new DatabaseSync call site by
    following the path it opens, and fails if a state.db handle drops
    readOnly. It also pins the one legitimately writable database.
  - i18n-parity compares the raw zh/en locale objects both ways. The
    existing coverage test merged en into zh at import time, so a key
    missing from zh could never fail there.

harness:check gains the four missing gates from the phase brief - retired
package directories, retired package scripts, a single UI library, and the
required root files. Each was verified to fail by mutating the repo.

The online-update channel had hardcoded upstream URLs. It now reads
HERMES_WEB_UI_VERSION_MANIFEST_URL and friends and degrades with a named
error, because a reimplementation has nowhere to pull releases from.

The remaining legacy strings are deliberate and each carries a reason in the
allow-list: the global-agent relay address and the OpenRouter referer are
load-bearing, the socket role identifier is a wire contract, and the pre-rename
DB filenames would orphan existing deployments if changed. AGENTS.md now says
so explicitly, so a future agent does not "clean them up".

Also removes a dead electron mock alias, an i18n exemption that had stopped
exempting anything, and a teardown race in plugins-view.test.ts where a-spin
animation frames outlived the jsdom environment.

Verified self-contained: with reference_code/ moved aside, harness:check,
build, test and test:e2e all pass, so the directory can now be deleted.

ARCHITECTURE.md

@@ -44,6 +44,9 @@ should not duplicate server persistence rules.
 - The project's own SQLite store under `packages/server/src/db` is the only writable
   store for sessions, messages, and usage. There is no startup import sync from
   Hermes state.
+- Every `state.db` handle in Node-side code opens with `readOnly: true`;
+  `tests/server/hermes-db-readonly.test.ts` classifies each `new DatabaseSync` call
+  site and fails if one of them drops the flag or opens it writable.
 - Uploads default to `config.uploadDir`, which is derived from the Web UI home unless `UPLOAD_DIR` is set.
 - Runtime data directories must also live under the Web UI home, not beside built `dist` assets.
 - Profile-scoped Hermes data should use existing profile helpers instead of manually joining paths.