drive: expose file approvals (start/approve/decline/reassign/cancel/comment) #196

Summary

Drive API file Approvals went GA 2026-04-21: a review/approve workflow on Drive files with methods start, approve, decline, reassign, cancel, and comment. gws drive doesn't expose any of this today.

Good news: ApprovalsService is already present in our pinned SDK (v0.267.0), so this does not strictly depend on the SDK bump (#195) — though we'll likely do it after the bump anyway.

Scope (net-new command surface)

Proposed drive subcommands (final naming TBD), one per API method plus listing/reading:

• drive approvals <file-id> — list approvals on a file
• drive approval <file-id> <approval-id> — get a single approval
• drive start-approval — start an approval (reviewers, due date, etc.)
• drive approve / drive decline — reviewer decisions
• drive reassign-approval — reassign reviewer
• drive cancel-approval — cancel
• drive comment-approval — add a comment to an approval

Notes

• Bigger feature than the chat items — multiple subcommands, request shaping for reviewers/decisions, and tests for each.
• Follow the standard pattern: command + runXxx in cmd/drive.go, register in init(), httptest tests, add to TestDriveCommands in cmd/commands_test.go, README table, version bump.
• Worth confirming the exact request/response schemas against the API reference before implementing.

References

• Release note: Drive API GA — approval management methods (2026-04-21)
• SDK: ApprovalsService already available in google.golang.org/api v0.267.0