Add inline note translation

[sato820]

Summary

Refs #206.

Adds inline note translation for feed and thread cells:

• shows a Translate control directly below eligible note text
• translates through a LibreTranslate-compatible endpoint
• uses the device preferred language as the default target language
• supports UserDefaults configuration for enabled state, endpoint URL, API key, and target language
• caches translations in memory for the current app session
• protects URLs, nostr references, Lightning invoices, Bitcoin addresses, hashtags, and handles from being modified by the translation provider
• handles reusable cells safely by ignoring stale translation callbacks

Notes

The default endpoint is https://libretranslate.com/translate; self-hosters or later Settings UI can set noteTranslationEndpointURL, noteTranslationAPIKey, noteTranslationTargetLanguage, and noteTranslationEnabled.

This keeps the implementation client-side and avoids adding backend cost for Primal.

Verification

• git diff --check
• Could not run xcodebuild or swift in this Windows environment; both tools are unavailable here.