feat: gdrive export ui integration

[Sentiaus]

What changes were proposed in this PR?

Wires the Drive export action into the three UI surfaces where download is currently available. The download button in each location has been converted to a dropdown with "Download" and "Export to Drive" (or "Connect to Drive" when not connected) options:

• Dashboard list items (list-item.component) — for workflows and datasets
• Dataset detail page (dataset-detail.component) — separate dropdowns for per-version ZIP download and per-file download
• Workflow editor menu (menu.component) — for the workflow JSON export button

All three surfaces:

• Call DriveService.getToken() on init to set initial connection state
• Subscribe to DriveService.onConnected() to update state live and show a "Google Drive connected" toast when the OAuth flow completes in the popup
• Show a "Exported to Google Drive" success toast on successful export
• Keep the dropdown button highlighted while the menu is open
• Fall back to connect() (or connect(true) on invalid_grant) when the user clicks "Connect to Drive" while not connected

Any related issues, documentation, discussions?

Closes #4240

How was this PR tested?

Unit tests added for all three components:

• list-item.component.spec.ts — Drive integration describe block: token status sets isDriveConnected, onConnected emission updates state and shows toast, connect() called when not connected, workflow and dataset export paths call exportToDrive and show success toast
• menu.component.spec.ts — Drive integration describe block: same connection state coverage, plus onClickDriveExportWorkflow serializes workflow content and shows success toast
• dataset-detail.component.spec.ts — new spec file: token status, onConnected toast, onClickDriveExportVersion and onClickDriveExportFile across connected/disconnected/missing-selection/success paths

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Sonnet 4.6

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.95%. Comparing base (d8c254c) to head (9f1dc6e).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5252      +/-   ##
============================================
- Coverage     48.95%   48.95%   -0.01%     
  Complexity     2377     2377              
============================================
  Files          1048     1048              
  Lines         40270    40264       -6     
  Branches       4272     4272              
============================================
- Hits          19714    19710       -4     
+ Misses        19402    19400       -2     
  Partials       1154     1154              

Flag	Coverage Δ		*Carryforward flag
access-control-service	39.53% <ø> (ø)
agent-service	33.76% <ø> (ø)		Carriedforward from d8c254c
amber	51.56% <ø> (-0.01%)	⬇️	Carriedforward from d8c254c
computing-unit-managing-service	0.00% <ø> (ø)
config-service	0.00% <ø> (ø)
file-service	37.99% <ø> (ø)
frontend	40.64% <ø> (-0.01%)	⬇️	Carriedforward from d8c254c
python	90.79% <ø> (ø)		Carriedforward from d8c254c
workflow-compiling-service	56.81% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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