feat: gdrive export frontend service integration

[Sentiaus]

What changes were proposed in this PR?

Adds the frontend service layer for Google Drive integration. No UI surfaces are changed in this PR — those are in the follow-up.

DriveService (drive.service.ts): New injectable service with four responsibilities:

• getToken() — calls GET /api/auth/google/drive/token and returns the connection status and short-lived access token
• connect(reauth?) — opens a popup to the /connect URL; emits on onConnected() when the OAuth flow completes
• onConnected() — observable that fires when the popup posts a gdrive-connected window message
• exportToDrive(blob, fileName) — opens the Google Picker folder selector, then uploads the blob to the chosen folder via the Drive multipart upload API

GoogleDriveConnectComponent: OAuth callback landing page at /gdrive-connect. Receives the authorization code from Google's redirect, posts a gdrive-connected message to the opener window, and closes itself.

Routing: Adds /gdrive-connect to the app router pointing at GoogleDriveConnectComponent.

index.html: Injects the gapi and Google Identity Services scripts needed by the Picker API.

Any related issues, documentation, discussions?

Closes #4240 (partial — UI wiring in follow-up PR)

How was this PR tested?

Unit tests in drive.service.spec.ts and google-drive-connect.component.spec.ts covering:

• getToken() returns status and access token
• connect() opens a popup and onConnected() emits on message receipt
• exportToDrive() calls the Drive multipart upload API and resolves

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 (9ebbe10).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5251      +/-   ##
============================================
- Coverage     48.95%   48.95%   -0.01%     
  Complexity     2377     2377              
============================================
  Files          1048     1048              
  Lines         40270    40269       -1     
  Branches       4272     4272              
============================================
- Hits          19714    19713       -1     
  Misses        19402    19402              
  Partials       1154     1154              

Flag	Coverage Δ		*Carryforward flag
access-control-service	39.53% <ø> (ø)
agent-service	33.76% <ø> (ø)		Carriedforward from a0b97fa
amber	51.56% <ø> (-0.01%)	⬇️	Carriedforward from a0b97fa
computing-unit-managing-service	0.00% <ø> (ø)
config-service	0.00% <ø> (ø)
file-service	37.99% <ø> (ø)
frontend	40.64% <ø> (ø)		Carriedforward from a0b97fa
python	90.79% <ø> (ø)		Carriedforward from a0b97fa
workflow-compiling-service	56.81% <ø> (ø)

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

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