feat(webview): add OpenAI Codex speed selector

[WebMad]

Responsibility and scope

Adds the OpenAI Codex speed selector in settings and its localized copy. Tests travel with the behavior in this PR.

Behavior and state handling

• The selector is wired through the buffered/cached settings callback.
• It does not mutate live extension state directly and does not send a direct postMessage; changes remain buffered until the existing Save flow applies them.
• Component tests cover rendering and settings interaction behavior.
• All 18 supported locale files are updated, with translation completeness covered.

Explicit non-goals

• No backend request-construction changes; those are isolated in the preceding PR.
• No unrelated Task.throttle.test.ts fix.
• No changeset.

Test evidence

• Focused component tests pass for the selector and cached settings callback.
• Translation completeness covers all 18 locale updates.
• Repository type checks passed from the push hook.
• The completed stack was locally verified before publication.

Stack dependency

1. Zoo-Code-Org/Zoo-Code#1040 — shared service-tier primitives.
2. WebMad/Zoo-Code#2 — backend persistence and request behavior.
3. This PR — webview selector, component tests, and 18 locales (base: WebMad:feat/openai-codex-fast-backend).

Review after #2; this PR intentionally contains only its immediate-base UI and localization delta.