feat(docx): improve docx tool — proper rich formatting instead of markdown wrapping

[EngineerProjects]

Context

The current docx tool (internal/tools/special/docx/) generates .docx files by wrapping markdown content using docxgo. In practice this produces documents that are essentially plain markdown wrapped in a Word container, without leveraging Word's native rich-text capabilities.

The tool has been disabled (removed from builtin.go) until a proper implementation is available.

What needs to be done

• Implement proper markdown → DOCX conversion that produces native Word formatting:
  • Headings → Word Heading 1/2/3 styles
  • Bold/italic → native character formatting
  • Tables → Word tables with proper column widths
  • Code blocks → monospace styled paragraphs
  • Lists → Word native list styles
• Consider using a more capable library (e.g. unioffice, go-docx, or calling pandoc as a subprocess when available)
• Add proper read action that extracts text from existing .docx files (currently relies on docling-serve)
• Re-enable the tool in builtin.go once the output quality is acceptable
• Add integration tests with fixture .docx files

Current implementation

File: internal/tools/special/docx/docx.go
Uses: github.com/mmonterroca/docxgo/v2

The tool was registered in internal/tools/builtin/builtin.go — removed in the commit that created this issue.