feat: add quick region OCR and selected-text translation

[xysamuel]

Summary

Adds two standalone text-action workflows alongside Snapok's existing image OCR and image translation:

• Quick region OCR (Control–Option–O): drag and release to recognize text locally with Apple Vision; choose preserved line breaks, smart paragraphs, or a single line.
• Selected-text translation (Control–Option–Shift–O): read accessible text selected in another application and translate using Baidu General Text Translation or the system on-device provider.
• Add configurable automatic copying, translucent multiline side notices, sound, editable results, and a menu action to review the last result.
• Add settings for providers, target languages, credentials, connection testing, language-pack preparation, and shortcuts; include English/Chinese UI, focused tests, and usage/privacy documentation.

Region OCR extracts text only; it does not automatically translate the captured region. This PR does not claim to introduce OCR or translation to Snapok for the first time.

Permissions, privacy, and compatibility

• Region capture uses Screen Recording permission; selected-text access uses Accessibility permission and depends on the source application exposing its selection.
• Region recognition stays local. Baidu translation sends selected text to Baidu over HTTPS and requires the user's own APP ID and secret; service quotas/charges may apply.
• Credentials use Keychain storage. Connection testing is explicit and separate from saving settings.
• The system text-translation implementation requires macOS 26+ and installed language packs.

Scope

Based on upstream dev at c7012ac. Contains 12 files: 11 feature/integration/test files and one usage document.

Explicitly excludes local code-signing certificate lookup/fallback changes, developer install/start scripts, local permission resets, unrelated component-snapping changes, and scrolling-stitch test changes. No dependency changes.

Validation

• Final staged git diff --check passed.
• Reviewed the isolated file list and integration diff; checked for private-key/token patterns, local paths, and local signing artifacts.
• Published tree and commit hashes exactly match the reviewed local commit.
• Build and automated-test success is not claimed: the interrupted session records invocations of the hotkey, localization, image-translation checks and swift build -c debug, but their final exit statuses/output were not retained in the resumed session. They were not rerun during this continuation.
• Reconfirm bash scripts/test-ocr.sh (default-language and English passes) and regression scripts in a reproducible environment.
• Manual release checks: multi-display capture, Escape cancellation, denied permissions, inaccessible selections, shortcut conflicts, and live translation with both providers.

The OCR suite uses injected translation functions and isolated pasteboards; it does not replace live-provider, language-pack, or cross-application permission testing.

Documentation

See docs/text-actions.md for usage, privacy, defaults, limitations, and testing instructions.