fix(sheets): handle commas in appendRows cell values

[mherod]

Summary

Fixes #118 — gwork sheets append now supports JSON array syntax for cell values containing commas.

Problem

appendRows used naive row.split(",") which broke values like "New York, NY" into separate cells.

Solution

Detect JSON array input ([...]) and parse it; fall back to comma-split for simple values (backward compatible).

# Old (broken for commas in values):
gwork sheets append <id> "Sheet1!A:C" "New York, NY,10001"  # 3 cells instead of 2

# New (use JSON array for values with commas):
gwork sheets append <id> "Sheet1!A:C" '["New York, NY","10001"]'  # correct: 2 cells

# Simple values still work:
gwork sheets append <id> "Sheet1!A:C" "Alice,30,NYC"  # still works

Test plan

• bunx tsc --noEmit — passes
• bun run lint — passes
• bun test --concurrent — 256/256 tests pass