feat(ai): add chart renderer, floating ball hook, and provider updates

- Add ai-chart-renderer for rendering charts in AI responses

- Add use-floating-ball hook for draggable AI assistant widget

- Update ai-assistant-widget, ai-chat-panel, ai-markdown-renderer, ai-provider-selector

- Update use-ai-chat-stream hook and prompt-templates service

src/modules/ai/services/prompt-templates.ts

@@ -165,6 +165,41 @@ export const CHAT_SYSTEM_PROMPT = [
   "Respond in the user's language (Chinese by default).",
   "Use Markdown formatting for structured content (lists, tables, code blocks).",
   "Be concise, accurate, and pedagogically sound.",
+  "",
+  "## Data Visualization",
+  "When presenting quantitative data, trends, comparisons, or distributions, ALWAYS render a chart using a fenced code block with one of these languages:",
+  "- ```chart:bar      — for comparing categories or showing distributions",
+  "- ```chart:line    — for trends over time",
+  "- ```chart:pie     — for part-to-whole / percentage breakdown",
+  "- ```chart:radar   — for multi-dimensional comparison (e.g. subject mastery)",
+  "",
+  "Chart spec format (JSON inside the code block):",
+  "```",
+  "{",
+  '  "title": "图表标题",',
+  '  "description": "可选说明",',
+  '  "data": [',
+  '    { "name": "数学", "score": 85, "fullTitle": "数学科目" }',
+  "  ],",
+  '  "xKey": "name",          // bar/line: X 轴字段；pie: nameKey',
+  '  "angleKey": "name",      // radar: 角度轴字段（可选，默认同 xKey）',
+  '  "series": [',
+  '    { "dataKey": "score", "name": "分数", "color": "hsl(221, 83%, 53%)" }',
+  "  ],",
+  '  "yDomain": [0, 100],     // 可选，Y 轴范围',
+  '  "height": 280,           // 可选，高度 px',
+  '  "showLegend": true       // 可选，多系列时建议 true',
+  "}",
+  "```",
+  "",
+  "Chart rules:",
+  "- Only use charts when data is genuinely quantitative (numbers, percentages, counts).",
+  "- Keep data arrays small (≤ 12 items) for readability.",
+  "- For pie charts, each data item must have a `name` and a `value` field; set series[0].dataKey to \"value\".",
+  "- For radar charts, set `angleKey` to the dimension name field and provide one series per metric.",
+  "- Colors are optional; if omitted, a colorblind-friendly palette is applied.",
+  "- Always provide a concise text explanation alongside the chart.",
+  "- Do NOT wrap the JSON in any other markdown; output the raw JSON inside the fenced block.",
 ].join("\n")
 
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