[APPS] Add OAuth auth for Apps dev server

[sdkennedy2]

Summary

Depends on #422.

Adds OAuth-aware authenticated request wiring for the Apps Vite dev server only:

• passes the resolved Apps auth method into the dev-server middleware
• reuses the Apps getAuthenticatedRequest helper and DoAuthenticatedRequest type
• returns a clear 403 for executeAction when API-key auth lacks credentials
• keeps debug bundle handling available without Datadog auth

Validation

• yarn workspace @dd/tests test:unit packages/plugins/apps/src/vite/dev-server.test.ts packages/plugins/apps/src/vite/index.test.ts packages/plugins/apps/src/index.test.ts
• yarn cli integrity
• git diff --check

[sdkennedy2]

@codex review
@cursor review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Delightful!

Reviewed commit: 7391f768ec

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[datadog-datadog-prod-us1]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 74e69b8 | Docs | Datadog PR Page | Give us feedback!}

[sdkennedy2]

Closing this because the Apps dev-server OAuth wiring has been folded back into #393 after collapsing the stack. #421 remains the separate optional-dependency integrity PR.