feat: interactive mindmap with expand/collapse, zoom, node-ask, multi-format export

[Anionex]

Summary

• Replace static Mermaid.js mindmap with interactive simple-mind-map library
• Merge two-step LLM pipeline into single-pass with improved knowledge-map prompt
• Add full mindmap interaction: expand/collapse all, zoom/pan/fit, node-level expand/collapse
• Add export: PNG (fully expanded with padding), hierarchical TXT, Mermaid code
• Add click-to-ask: click node → contextual question popover (2 options) → auto-fill chat input
• Fix preview modal missing rounded corners and backdrop blur
• Prompt retains concrete data/numbers, adapts to article type

Changes

• Backend: Single-pass prompt with data-aware generation, max_depth=6 (route + state aligned)
• Frontend: New MindMapPreview component, mermaidToMarkdown/markdownToMermaid utils, TS declarations
• Dependencies: +simple-mind-map, -mermaid

Commits

1. edfb7d0 — Backend: single-pass prompt + max_depth=6
2. 9e8faff — Dependencies + format conversion utils + TS declarations
3. a5fbc3e — MindMapPreview component + interactions + modal fix
4. 4d438b3 — Code review fixes (debug logs, dead state, deps)
5. 29e9656 — PNG export truncation fix (padding + fit before capture)

Test plan

• Generate mindmap from uploaded document, verify interactive rendering
• Test expand/collapse all buttons and node-level expand/collapse
• Test zoom (scroll), pan (drag), fit button
• Export PNG, TXT, Mermaid and verify output
• Click node → verify popover with 2 question options
• Select question → verify modal closes, chat input filled, input focused
• Open old .mmd files in knowledge base → verify backward compatibility
• PNG export captures full content without truncation