release: align beta.8 with DSH rc1 accessibility candidate 5

[mattheliu]

Summary

• advance the companion to 0.1.0-beta.8 against the exact official @deepseek-ai/dsh@0.1.2-rc.1 baseline
• pin assembled CI and the public AT lab to immutable core tag dsh-v0.1.2-rc.1-a11y.5
• archive and validate clean three-engine core evidence for revision 1e7f105934eeb8d93dedcf738c480fab30069109 without replacing earlier records
• update the bilingual compatibility, install, roadmap, and evidence documentation

Local validation

• typecheck: passed
• unit/schema tests: 224 passed
• human-evidence validator: passed (ledger still contains templates only)
• production build: passed
• npm pack dry run: 123 files
• assembled Chromium/Firefox/WebKit protocol: 5 passed
• disposable AT lab smoke: passed

Evidence boundary

This is automated browser, packaging, and lab-readiness evidence. It does not claim listener-verified VoiceOver/NVDA output, braille/switch/voice-input support, WCAG certification, or independent disabled-developer task completion.