fix(i18n-ja): improve the Japanese text translation for Edge-Drop

[zibasan]

Purpose

This PR refines the Japanese translations in edge-drop-translations/ja.json and updates the compiled translation dictionary (src/i18n/translations.ts).

The update replaces literal/awkward translations across settings, system tray menus, onboarding guides, toasts, and UI controls with natural, user-friendly Japanese terminology commonly found in modern desktop applications.

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Key Improvements

1. User-Friendly Terminology:
   • Replaced technical jargon and transliterations with intuitive UI terms (e.g., シェルフ (shelf) -> パネル (panel), エッジ placement -> 表示位置 (position), シークレット -> クリップボードの取得を一時的に停止).
2. Consistent Tone & Phrasing:
   • Standardized sentence endings across settings and dialogs to use polite, helpful Japanese (-します / -です) for better usability.
3. Clearer Descriptions & Onboarding Instructions:
   • Reworded feature descriptions (autoDeleteDesc, capacityDesc, hoverActivationDescOn) and interactive onboarding steps (ungroupDesc, mergeDesc, proTips) so users can easily understand how configuration options and drag-and-drop gestures work.
4. Clean & Concise Labels:
   • Simplified overly wordy context menu items and toast notifications (e.g., エクスプローラーで場所を開く -> エクスプローラーで開く).

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Representative Examples (Before / After)

Here are representative examples showcasing the improvements made in this PR:

Key / Scope	Before	After	Improvement Note
behaviour.hoverActivationTitle	ホバー有効化	ホバー時に表示する	Clearer feature name
behaviour.autoDeleteDesc	コピーした項目を自動的に消去 (ピン留めは保持)	未ピン留めのクリップボードアイテムを指定時間後に自動で削除します	Precise & polite description
position.edgePlacementTitle	エッジ配置	表示位置	Standard desktop UI term
item.copyTypeHint	{type} をコピーするか「すべて」に戻ってください	{type} をコピーするか、フィルターを「すべて」に切り替えてください	Natural empty state guidance
welcome.ungroupDesc	スタック内の項目を分割したい？...	スタック内の項目を個別に取り出したい場合は、...	Smooth onboarding instructions
tray.showClipboard	クリップボードを表示	パネルを表示	Unified panel terminology
flyout.openInExplorer	エクスプローラーで場所を開く	エクスプローラーで開く	Concise context menu label
toast.itemUnpinned	項目のピンを解除しました	項目のピン留めを解除しました	Standard phrasing for pin actions

* And other minor phrasing refinements across ja.json.

Verification

• Ran node scripts/generate_translations_ts.cjs to compile edge-drop-translations/ja.json into src/i18n/translations.ts.
• Ran npm run typecheck to confirm no TypeScript errors in src/i18n/translations.ts.
• Verified UI rendering locally using npm run dev.

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I would appreciate it if you could leave a review. Thank you.

[Deepender25]

@zibasan thanks a lot for this as I am not a native speaker of all these languages supported in edge drop I know there will be imperfections I will look into it.