feat: drive reporting/sync + contacts dedupe

[rohan-patnaik]

Summary

• Add Drive reporting commands (tree, du, inventory) with path-based output and size/modified metadata.
• Add Drive sync (pull/push) with dry-run, include/exclude filters, checksum support, delete safeguards, and a local state file.
• Add contacts dedupe with preview/apply workflow and merge rules.
• Add tests and README examples for the new commands.

Testing

• go test ./...

Notes

• Sync state is stored locally in .gog-sync.json (no secrets).
• Google Docs are exported on pull and skipped on push.
• I’m new to OSS contributions — happy to adjust or split this if you prefer.

[visionik]

hi @rohan-patnaik - I like what you've done here, thank you. I'm helping peter get gogcli PR's and issues addressed quickly. Since it's been a while, the merge for this --> main is complex. could you rebase from main and resubmit the PR? Thank you!

[rohan-patnaik]

Rebased onto the latest main and resolved conflicts. Branch is updated and ready for another pass. Thanks!

[visionik]

@rohan-patnaik Looking good. Ci/test would like some lint cleanups:

https://github.com/steipete/gogcli/actions/runs/22588136930/job/65478928149?pr=116

[rohan-patnaik]

Addressed the CI lint cleanup items and pushed an update.

Validation run locally:

• make lint (0 issues)
• go test ./... (all packages passing)