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.

tests/client/markdown-rendering.test.ts

@@ -269,7 +269,7 @@ describe('MarkdownRenderer', () => {
   it('renders local mov links as inline video players', () => {
     const wrapper = mount(MarkdownRenderer, {
       props: {
-        content: '[录屏2026-05-08 15.19.46.mov](/Users/ekko/Desktop/录屏2026-05-08%2015.19.46.mov)',
+        content: '[录屏2026-05-08 15.19.46.mov](/Users/tester/Desktop/录屏2026-05-08%2015.19.46.mov)',
       },
     })
 
@@ -277,7 +277,7 @@ describe('MarkdownRenderer', () => {
     expect(video.exists()).toBe(true)
     expect(video.attributes('src')).toContain('/api/hermes/download?path=')
     const src = new URL(video.attributes('src'))
-    expect(decodeURIComponent(src.searchParams.get('path') || '')).toBe('/Users/ekko/Desktop/录屏2026-05-08 15.19.46.mov')
+    expect(decodeURIComponent(src.searchParams.get('path') || '')).toBe('/Users/tester/Desktop/录屏2026-05-08 15.19.46.mov')
     expect(wrapper.find('.markdown-video-footer .att-name').text()).toBe('录屏2026-05-08 15.19.46.mov')
   })