feat: read/write native YAML and CPS files directly in Google Drive

[pskillen]

Problem

Users currently move files in and out of the tools by hand (local file pick/download). For people who keep their codeplugs in Google Drive, that means a manual download/upload round-trip every time, and no shared source of truth across devices.

Intended outcome

Let users read and write files directly in Google Drive from within the tools:

• Open native YAML files (feat: native YAML import and export #10) directly from Google Drive.
• Open CPS-specific files (vendor CSV exports) directly from Google Drive.
• Save/export back to Google Drive in the same formats.
• Sensible auth/connect flow scoped to browser-local credentials only.

Affected tool(s)

• Shared import/export + storage code consumed by tools/.

Notes

• Stay static (HTML + sidecar JS), no bundler unless asked.
• Privacy: OAuth tokens/credentials stay in browser LocalStorage only, never in the repo; never commit operator codeplugs.
• Depends on native YAML import/export (feat: native YAML import and export #10) and CPS export (feat: CPS export support (internal models → vendor format) #8); complements LocalStorage persistence (feat: persist state in browser LocalStorage #9) and the internal data models from genericise-import (feat: genericise CPS import via internal data models #7).
• Related: feat: native YAML import and export #10, feat: persist state in browser LocalStorage #9, feat: CPS export support (internal models → vendor format) #8, feat: genericise CPS import via internal data models #7.