fix(web): localize artifact preview controls and errors

[testikun]

Problem

Refs #350. In the Chinese Web workbench, the file-preview dialog still used English for its title, actions, read-only/version details, truncation notice, accessibility names, and artifact failures.

Value

The preview can be inspected and operated consistently in the active language without changing the file contents or the authority of the read-only artifact path.

Approach

• Use the existing react-i18next catalogue for preview-only UI text and known ARTIFACT_* errors. Preserve unknown server diagnostics verbatim.
• Keep the underlying error until render so a language change while the panel is open reprojects its text without repeating a request.
• Assign typed artifact error codes to two local download failures. Do not change Host receipts, file bytes, refresh, or download semantics.
• Retain the built Web asset. This is a partial feat(web): add persistent theme/language preferences and accessibility/mobile hardening #350 fix; theme, language persistence, and broader mobile/a11y work remain separate.

Validation

• bun run check: passed (config/docs/discipline, Web build/typecheck, format, lint, TypeScript).
• bun run test: Node 1658 passed, 1 platform skip; Vitest 221 passed.
• Focused vitest run tests/web/evidence-view.spec.ts: 6/6 after removing an unnecessary test Provider wrapper (ablation).
• Real Chrome playwright test --config tests/web/playwright.config.ts tests/web/artifact-evidence.e2e.ts: 1/1, zh-CN fixture, verified download, refresh, missing-file error, and axe checks. No model call.
• Source identity: upstream main@f6b49ae59605b1276b8267f2886d22c03f01533c; isolated pi list showed the single OpenPI source at this worktree. No claim about an npm-installed runtime.

Before (Chinese page, English preview):

After (same fixture, Chinese preview):

Impact

• User-visible: file-preview controls, status, and known artifact errors follow the current language; file contents remain unchanged.
• Model-visible context/tools: none.
• Runtime/lifecycle and persisted config/data: none.
• Compatibility/risk: local download errors now carry typed WebApiError codes; unknown error messages continue to display their original diagnostics. Other Web surfaces and language preference ownership are unchanged.