feat: add docs update command for editing Google Docs

[goncaloalves]

Summary

This PR adds comprehensive markdown support to gog docs update and gog slides commands, enabling rich formatting conversion from markdown to native Google Docs/Slides elements.

Features Added

📄 Docs Update Command (gog docs update)

Core functionality:

• Replace entire document content or append to existing
• Support for plain text and markdown formats

Markdown → Google Docs conversion:

• ✅ Headings (H1-H6) → Native heading styles
• ✅ Bold (**text**) → Bold formatting
• ✅ Italic (*text*) → Italic formatting
• ✅ Inline code (`code`) → Monospace font
• ✅ Links ([text](url)) → Clickable hyperlinks
• ✅ Lists (- item, * item, 1. item) → Bullet/numbered lists
• ✅ Code blocks (```) → Monospace + gray background
• ✅ Blockquotes (> text) → Indented paragraphs
• ✅ Horizontal rules (---, ***, ___) → Separator lines
• ✅ Tables → Native Google Docs tables (with header row bold)

Table support:

• Native Google Docs tables (not formatted text!)
• Multi-step API: insert table → fetch indices → populate cells
• Header rows automatically bold
• Proper cell alignment

📊 Slides Commands (gog slides)

New commands:

• gog slides create — Create new presentation
• gog slides update — Update slides with markdown content
• gog slides template — Create from templates (--template flag)

Markdown → Google Slides conversion:

• Title slides (first H1 becomes slide title)
• Bullet points
• Code blocks
• Bold/italic text

Usage Examples

# Update document with markdown file
gog docs update <docId> --content-file ./document.md --format markdown

# Append to existing document
gog docs update <docId> --content "## New Section\n\nContent here." --append

# Create presentation from markdown
gog slides create "My Presentation" --content-file ./slides.md

# Create from template
gog slides create "Quarterly Report" --template quarterly

Technical Details

UTF-16 Indexing:
Google Docs API uses UTF-16 code units for character positions. This PR correctly handles multi-byte characters (emojis, special characters) by using utf16Len() instead of byte length.

Native Table Insertion:
Tables require multi-step operations:

1. Insert table structure via InsertTableRequest
2. Fetch document to retrieve cell indices
3. Insert text into each cell at calculated positions
4. Apply header row formatting (bold)

See docs_table_inserter.go for implementation.

Files Changed

File	Changes
internal/cmd/docs.go	Docs update command + table insertion
internal/cmd/docs_formatter.go	Markdown → Docs requests converter
internal/cmd/docs_markdown.go	Markdown parser
internal/cmd/docs_markdown_test.go	Parser tests
internal/cmd/docs_table_inserter.go	Native table insertion (NEW)
internal/cmd/slides.go	Slides commands
internal/cmd/slides_formatter.go	Markdown → Slides converter
internal/cmd/slides_markdown.go	Slides markdown parser
internal/googleapi/slides.go	Slides API helpers
internal/googleauth/service.go	Added Slides scope

Stats

• +2,222 lines added
• -59 lines removed
• 12 files changed
• 10 commits

Testing

Tested with real documents including:

• Docker course documentation (21KB, emojis, diagrams)
• Research documents with tables
• Presentation slides with markdown formatting

All inline formatting (bold, italic, code, links) working correctly with UTF-16 indexing.

---

Built with 🔪 by Jarbas (Gonçalo's AI assistant)

[steipete]

Landed via temp rebase onto main.

• Gate: make ci
• Land commit: d2db0cc
• Merge commit: 7945602

Thanks @goncaloalves!