feat(ui): tidy the start screen and the chat panel details (#962)

Start screen
- The five examples are one row of picture tiles (title under the picture); the old cards cut their descriptions off with an ellipsis
- "Open .drawio file" leaves the example grid and sits with "Start with a blank canvas" below it, both as outlined buttons
- The "Paper to diagram" example gets a thumbnail of its result (public/paper_demo.svg) like the other four
- The caption says what happens: examples use saved answers, so they appear at once and do not call the AI
- Shorter lede

Chat panel
- The version card's "</>" icon button becomes a "Show XML" text link in the summary line; the summary runs under the title row, so Undo is the card's only button
- Settings uses the gear icon; new diagram uses a file-plus icon instead of the pen that reads as "edit"
- The message box has the same side padding as the message column

Copy
- The model picker says "Server model" instead of "Default" when the server's model is in use
- The theme description no longer claims the diagram always stays on a white sheet (the canvas follows the theme)
- en, zh, ja and zh-Hant dictionaries updated together

lib/i18n/dictionaries/en.json

@@ -72,7 +72,7 @@
         "replicateDescription": "Upload and replicate an existing flowchart",
         "creativeDrawing": "Creative drawing",
         "creativeDescription": "Draw something fun and creative",
-        "cachedNote": "Examples open instantly and don't use your model.",
+        "cachedNote": "Examples use saved answers: they appear instantly and don't call the AI.",
         "mcpServer": "MCP Server",
         "mcpDescription": "Use in Claude Desktop, VS Code & Cursor"
     },
@@ -96,7 +96,7 @@
         "language": "Language",
         "languageDescription": "Choose your interface language.",
         "theme": "Theme",
-        "themeDescription": "Light or dark interface. The diagram always stays on a white sheet, the way it exports.",
+        "themeDescription": "Light or dark interface. The canvas follows the same theme.",
         "diagramStyle": "Diagram style",
         "diagramStyleDescription": "How the AI draws new diagrams: Styled uses colors and icons, Minimal keeps shapes plain.",
         "sendShortcut": "Send shortcut",
@@ -399,7 +399,7 @@
         "searchModels": "Search models...",
         "noModelsFound": "No models found.",
         "default": "Default",
-        "serverDefault": "Server Default",
+        "serverDefault": "Server model",
         "serverModels": "Server Models",
         "userModels": "User Models",
         "configureModels": "Configure Models...",
@@ -694,7 +694,7 @@
     },
     "lobby": {
         "title": "What would you like to draw?",
-        "lede": "Describe a diagram, or upload a screenshot or PDF. You get a regular draw.io diagram that you can keep editing and export.",
+        "lede": "Describe a diagram or upload a screenshot or PDF. You get a draw.io diagram you can keep editing and export.",
         "placeholder": "For example: a login sequence diagram with SMS codes and retries",
         "recent": "Recent diagrams",
         "drawYourself": "Start with a blank canvas",

lib/i18n/dictionaries/ja.json

@@ -72,7 +72,7 @@
         "replicateDescription": "既存のフローチャートをアップロードして複製",
         "creativeDrawing": "自由なイラスト",
         "creativeDescription": "楽しくてクリエイティブなものを描く",
-        "cachedNote": "例はすぐに開き、モデルは使いません。",
+        "cachedNote": "例は保存済みの回答を使うので、すぐに表示され、AI を呼び出しません。",
         "mcpServer": "MCP サーバー",
         "mcpDescription": "Claude Desktop、VS Code、Cursor で使用"
     },
@@ -96,7 +96,7 @@
         "language": "言語",
         "languageDescription": "インターフェース言語を選択します。",
         "theme": "テーマ",
-        "themeDescription": "画面をライトにするかダークにするか。図はエクスポートしたときと同じく、常に白い用紙の上に表示されます。",
+        "themeDescription": "画面をライトにするかダークにするか。キャンバスも同じテーマになります。",
         "diagramStyle": "図のスタイル",
         "diagramStyleDescription": "AI が新しい図を描くときのスタイル。スタイル付きは色やアイコンを使い、ミニマルは素朴な図形だけにします。",
         "sendShortcut": "送信のショートカット",
@@ -354,7 +354,7 @@
         "searchModels": "モデルを検索...",
         "noModelsFound": "モデルが見つかりません。",
         "default": "デフォルト",
-        "serverDefault": "サーバーデフォルト",
+        "serverDefault": "サーバーのモデル",
         "serverModels": "サーバーモデル",
         "userModels": "ユーザーモデル",
         "configureModels": "モデルを設定...",
@@ -694,7 +694,7 @@
     },
     "lobby": {
         "title": "どんな図を描きますか？",
-        "lede": "図の内容を説明するか、スクリーンショットや PDF をアップロードしてください。できあがるのは通常の draw.io の図なので、続けて編集もエクスポートもできます。",
+        "lede": "図を説明するか、スクリーンショットや PDF をアップロードしてください。できあがるのは編集もエクスポートもできる draw.io の図です。",
         "placeholder": "例：SMS 認証とリトライを含むログインのシーケンス図",
         "recent": "最近の図",
         "drawYourself": "白紙のキャンバスから始める",

lib/i18n/dictionaries/zh-Hant.json

@@ -72,7 +72,7 @@
         "replicateDescription": "上傳並複製現有流程圖",
         "creativeDrawing": "創意繪畫",
         "creativeDescription": "繪製有趣且富有創意的內容",
-        "cachedNote": "範例會立即開啟，不呼叫模型。",
+        "cachedNote": "範例使用保存好的答案，立即顯示，不呼叫 AI。",
         "mcpServer": "MCP 伺服器",
         "mcpDescription": "在 Claude Desktop、VS Code 和 Cursor 中使用"
     },
@@ -96,7 +96,7 @@
         "language": "語言",
         "languageDescription": "選擇介面語言。",
         "theme": "主題",
-        "themeDescription": "介面用淺色還是深色。圖紙始終是白底，和匯出後的樣子一致。",
+        "themeDescription": "介面用淺色還是深色，畫布跟隨同一主題。",
         "diagramStyle": "圖形風格",
         "diagramStyleDescription": "AI 畫新圖時的風格：精緻會用顏色和圖示，簡約只用樸素的圖形。",
         "sendShortcut": "傳送快速鍵",
@@ -399,7 +399,7 @@
         "searchModels": "搜尋模型...",
         "noModelsFound": "未找到模型。",
         "default": "預設",
-        "serverDefault": "伺服器預設",
+        "serverDefault": "伺服器模型",
         "serverModels": "伺服器模型",
         "userModels": "使用者模型",
         "configureModels": "配置模型...",
@@ -694,7 +694,7 @@
     },
     "lobby": {
         "title": "說說你要畫什麼",
-        "lede": "描述一張圖，或上傳截圖、PDF。畫出來的是標準的 draw.io 圖表，可以接著改，也可以匯出。",
+        "lede": "描述一張圖，或上傳截圖、PDF。得到的是可以繼續編輯和匯出的 draw.io 圖。",
         "placeholder": "例如：使用者登入的時序圖，包含簡訊驗證碼和失敗重試",
         "recent": "最近的圖紙",
         "drawYourself": "從空白畫布開始",

lib/i18n/dictionaries/zh.json

@@ -72,7 +72,7 @@
         "replicateDescription": "上传并复制现有流程图",
         "creativeDrawing": "创意绘画",
         "creativeDescription": "绘制有趣且富有创意的内容",
-        "cachedNote": "示例会立即打开，不调用模型。",
+        "cachedNote": "示例使用保存好的答案，立即显示，不调用 AI。",
         "mcpServer": "MCP 服务器",
         "mcpDescription": "在 Claude Desktop、VS Code 和 Cursor 中使用"
     },
@@ -96,7 +96,7 @@
         "language": "语言",
         "languageDescription": "选择界面语言。",
         "theme": "主题",
-        "themeDescription": "界面用浅色还是深色。图纸始终是白底，和导出后的样子一致。",
+        "themeDescription": "界面用浅色还是深色，画布跟随同一主题。",
         "diagramStyle": "图形风格",
         "diagramStyleDescription": "AI 画新图时的风格：精致会用颜色和图标，简约只用朴素的图形。",
         "sendShortcut": "发送快捷键",
@@ -399,7 +399,7 @@
         "searchModels": "搜索模型...",
         "noModelsFound": "未找到模型。",
         "default": "默认",
-        "serverDefault": "服务器默认",
+        "serverDefault": "服务器模型",
         "serverModels": "服务器模型",
         "userModels": "用户模型",
         "configureModels": "配置模型...",
@@ -694,7 +694,7 @@
     },
     "lobby": {
         "title": "说说你要画什么",
-        "lede": "描述一张图，或者上传截图、PDF。画出来的是标准的 draw.io 图表，可以接着改，也可以导出。",
+        "lede": "描述一张图，或上传截图、PDF。得到的是可以继续编辑和导出的 draw.io 图。",
         "placeholder": "比如：用户登录的时序图，包含短信验证码和失败重试",
         "recent": "最近的图纸",
         "drawYourself": "从空白画布开始",