feat: add programmatic command API for AI-driven document editing

[ant-louis]

Summary

Add a file-based IPC system that enables external tools (like AI agents) to programmatically edit DOCX documents via JSON commands written to .superdoc/{docname}.json.

Commands added

• getText - Read document content (text/html/both formats)
• getNodes - Get document structure by node type (paragraph, heading, table, etc.)
• replaceText - Find and replace with track changes support
• insertContent - Insert content at anchor positions (before/after text)
• formatText - Apply formatting (font, color, bold, italic, links, highlight)
• insertImage - Insert images from URL or file path (auto base64 conversion)
• insertTable - Create tables with optional data population
• deleteNode - Delete nodes by type and index
• addComment - Add comments to text ranges
• undo/redo - History navigation

Key features

• File-based communication via .superdoc/{docname}.json
• Track changes support (suggesting mode) for content edits
• Configurable author attribution for changes
• Image URL/path to base64 conversion handled by extension

Example usage

# Read document content
echo '{"id":"1","command":"getText","args":{"format":"text"}}' > .superdoc/contract.json

# Replace text with track changes
echo '{"id":"2","command":"replaceText","args":{"search":"2024","replacement":"2025"}}' > .superdoc/contract.json

# Add a comment
echo '{"id":"3","command":"addComment","args":{"search":"confidential","comment":"Needs legal review"}}' > .superdoc/contract.json

Test plan

• Open a DOCX file in VS Code with SuperDoc
• Write a getText command to .superdoc/{docname}.json
• Verify response is written back to the same file
• Test replaceText and verify track changes appear
• Test addComment and verify comment balloon appears
• Export DOCX and verify changes persist in Word