feat(i18n): Hebrew (he-IL) translation + RTL layout support

[cdtauman]

Description:

Adds a full Hebrew (he-IL) translation, end-to-end Right-to-Left (RTL) layout support, and externalizes the remaining hardcoded UI strings into the en-US dictionary so the whole app can be localized. Rebased cleanly on the latest main.

This supersedes #488 (which had merge conflicts and unsigned commits). This branch is rebased on current main with no conflicts and a single DCO Signed-off-by commit.

Related Issue:

None.

Changes Made:

• Hebrew localization: new he-IL.json with 100% key parity to en-US.json (829/829 keys, 0 missing / 0 extra). Hebrew added to the language selector.
• RTL engine: isRTL computed in the i18n store + a watcher that toggles document.documentElement.dir (rtl/ltr) and lang on language change.
• Logical CSS: migrated directional Tailwind utilities to logical properties (ml/mr → ms/me, left/right → start/end, pl/pr → ps/pe) across components so layouts mirror correctly in RTL.
• String externalization: replaced remaining hardcoded English text with languages.* keys across App, Chat, PromptArea, settings, dialogs, history and preset components; added the matching en-US keys as a foundation for future languages.
• Helpers: added preset / variant / tag translation helpers in lib/utils.ts.
• Layout: long translated labels now wrap instead of truncating in workflow settings.

Testing Done:

• vue-tsc --noEmit (type-check): passes, 0 errors.
• eslint . (lint:ci): passes, 0 errors.
• prettier --check . (format:ci): passes.
• Verified en-US / he-IL key parity (829/829, 0 missing, 0 extra).
• Manually toggled English (LTR) ↔ Hebrew (RTL) and confirmed the layout mirrors.

Screenshots:

N/A (text/layout changes) — can add on request.

Checklist:

• I have tested the changes locally.
• I have self-reviewed the code changes.
• I have updated the documentation, if necessary.

[cdtauman]

@qiacheng @mschuettlerTNG — would appreciate your review when you have a moment.

A few notes that may help:

• This is a purely additive change to en-US.json (no existing keys renamed or removed) and a new he-IL.json file.
• The RTL layout work uses logical CSS properties (ms-*/me-*, start-*/end-*) which are a no-op for existing LTR languages — existing users won't notice any difference.
• All three CI gates pass locally: vue-tsc, eslint, and prettier.

Happy to split into a smaller RTL-infrastructure-only PR (store watcher + logical CSS migration, ~20 files) if that's easier to review first, with the Hebrew dictionary as a follow-up.

Note on base branch: I targeted main because the dev branch referenced in CONTRIBUTING no longer exists in this repo.

[cdtauman]

Screenshots

Hebrew (RTL) — עברית

Main UI	Chat Settings	Image Settings

English (LTR) — same screens for comparison

Main UI	Image Settings	Chat Settings

Key observations:

• All buttons, labels, and layout elements flip correctly to the right side in RTL.
• Labels wrap gracefully instead of truncating (visible in settings panels).
• Switching back to English instantly restores LTR — no page reload needed.
• Existing LTR languages are completely unaffected.