Add sidekick summaries to E2E staging configs

[alfonso-noriega]

WHY are these changes introduced?

The multi-config app dev E2E tests create a synthetic shopify.app.staging.toml fixture that no longer matches the required app config shape used by app dev.

The default fixture already includes Sidekick metadata, but the in-test staging config did not. That made the E2E scenario fail before it could validate the actual behavior under test: selecting the correct app config with and without -c.

WHAT is this pull request doing?

Adds a minimal [sidekick] section with extensions_summary to the generated staging TOML in packages/e2e/tests/multi-config-dev.spec.ts for both multi-config E2E cases.

This keeps the staging config aligned with the valid app fixture while preserving the test intent:

• app dev -c staging loads shopify.app.staging.toml
• app dev without -c continues to load shopify.app.toml

How to test your changes?

Run the affected E2E spec:

pnpm --filter e2e test tests/multi-config-dev.spec.ts

Or run the E2E workflow/check that covers multi-config app dev.

Post-release steps

None.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows) — test fixture TOML only.
• I've considered possible documentation changes — none needed.
• I've considered analytics changes to measure impact — none.
• The change is not user-facing — no changeset required.

[alfonso-noriega]

• Fix auto-upgrade telemetry reporting order #7670
• Add sidekick summaries to E2E staging configs #7752 👈 (View in Graphite)
• main

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