Summary

Adds support for Google Docs tabs (multi-tab documents) and document editing commands.

Tab support

• docs list-tabs <docId> — List all tabs with ID, title, and index
• docs cat <docId> --all-tabs — Print all tabs with === Tab: <title> === headers
• docs cat <docId> --tab <title|id> — Print a specific tab by title or tab ID

Document editing commands

• docs write <docId> [content] — Write/append content to a doc (supports --replace, --file, --markdown)
• docs insert <docId> [content] — Insert text at a specific character --index
• docs delete <docId> — Delete text range with --start/--end
• docs find-replace <docId> <find> <replace> — Find and replace with optional --match-case

Key behaviors

• Default docs cat (no flags) is fully backward compatible — no API behavior changes
• Tab lookup supports exact ID match (t.abc123) and case-insensitive title match ("My Tab")
• Nested/child tabs are flattened and included in all operations
• JSON output (--json) supported for all tab and editing operations
• Uses the Docs API IncludeTabsContent(true) parameter only when tab flags are specified
• Write supports content from argument, --file, or stdin
• Markdown mode (--markdown --replace) uses Drive API for native format conversion

Example usage

# List tabs in a document
gog docs list-tabs 1QHIRX8hGeiWiaN...

# Read all tabs
gog docs cat 1QHIRX8hGeiWiaN... --all-tabs

# Read a specific tab by title
gog docs cat 1QHIRX8hGeiWiaN... --tab "Planning"

# Append text to a document
gog docs write 1QHIRX8hGeiWiaN... "Hello, world!"

# Replace document content with markdown
gog docs write 1QHIRX8hGeiWiaN... --file content.md --markdown --replace

# Insert text at the beginning
gog docs insert 1QHIRX8hGeiWiaN... --index 1 "Prepended text"

# Delete a range
gog docs delete 1QHIRX8hGeiWiaN... --start 10 --end 50

# Find and replace
gog docs find-replace 1QHIRX8hGeiWiaN... "TODO" "DONE" --match-case

Closes #125

Test plan

• 12 new tests covering all tab operations
• Backward compatibility test: default cat does NOT send includeTabsContent
• --tab/--all-tabs sends includeTabsContent=true
• Tab-by-title (case-insensitive) and tab-by-ID lookup
• Nested child tabs flattened correctly
• JSON output for --tab, --all-tabs, and list-tabs
• Tab-not-found error handling
• Full test suite passes (all existing tests unaffected)
• Lint passes clean (0 issues)

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