feat(sheets): add conditional-format, banding, and chart list commands

[codBang]

Summary

Adds first-class Sheets advanced formatting command groups to gog:

• gog sheets conditional-format (add, list, clear)
• gog sheets banding (set, clear)
• gog sheets chart list

This closes a common automation gap where users need rule-based styling (conditional formats + alternating colors) instead of one-off manual coloring.

Why

Current gog sheets supports values/metadata/basic format, but lacks wrappers for advanced spreadsheets.batchUpdate operations. In real workflows this blocks:

• Tier/status color rules that auto-apply to new rows
• Alternating row banding for readability
• Scriptable chart inventory for dashboard automation

What changed

• Extended SheetsCmd registry in internal/cmd/sheets.go
  • added conditional-format, banding, chart
• Added internal/cmd/sheets_advanced.go implementing:
  • SheetsConditionalFormatAddCmd
  • SheetsConditionalFormatListCmd
  • SheetsConditionalFormatClearCmd
  • SheetsBandingSetCmd
  • SheetsBandingClearCmd
  • SheetsChartListCmd
• Added dry-run support for new mutating commands (--dry-run --json)

Validation

Local checks run:

• go build -o ./bin/gog ./cmd/gog ✅
• go test ./internal/cmd -run 'Sheets|sheet' ✅
• CLI surface smoke checks ✅
  • ./bin/gog sheets --help
  • ./bin/gog sheets conditional-format --help
  • ./bin/gog sheets banding --help
  • ./bin/gog sheets chart --help

Dry-run behavior checks ✅

• ./bin/gog sheets conditional-format add ... --dry-run --json --no-input
• ./bin/gog sheets banding set ... --dry-run --json --no-input

Notes

• This PR intentionally scopes chart support to list first (inventory/inspection).
• chart create/update can be added incrementally in a follow-up PR once spec defaults are finalized.

Example usage

# Add A-tier highlight rule
gog sheets conditional-format add <sheetId> \
  --range 'Pipeline!A2:H999' \
  --type text-eq \
  --expr A \
  --style-json '{"backgroundColor":{"red":1,"green":0.8588,"blue":0.4275}}'

# List rules
gog sheets conditional-format list <sheetId> --json

# Remove all rules from a sheet
gog sheets conditional-format clear <sheetId> --sheet Pipeline --all

# Apply alternating banding
gog sheets banding set <sheetId> --range 'Pipeline!A1:H999'

# List embedded charts
gog sheets chart list <sheetId> --json