Add new App Doctor agent checks

[lopez-mar]

WHY are these changes introduced?

App Doctor's current agentic pack does not have dedicated checks for lifecycle/replay failures, dependency reachability, or upload-to-active-preview execution paths. These are separate from the prompt refinements in #8495 and deserve their own review surface.

WHAT is this pull request doing?

Adds three new App Doctor agent checks:

• SESSION_LIFECYCLE_AND_REPLAY
• DEPENDENCY_REACHABILITY
• ACTIVE_UPLOADS_AND_PRIVILEGED_PREVIEWS

Also registers the new stable IDs in the App Doctor catalog, regenerates the embedded prompt bundle, updates prompt-loading tests from 31 to 34 checks, and adds a patch changeset.

The active-upload prompt is intentionally bounded to complete upload-to-active-render paths and does not report storage/header hygiene alone.

How to test your changes?

pnpm --filter @shopify/app generate:app-doctor-checks
pnpm exec vitest run packages/app/src/cli/services/app-doctor-engine/tests/checks.test.ts packages/app/src/cli/services/app-doctor-engine/tests/registry.test.ts packages/app/src/cli/services/app-doctor-engine/tests/scan-contract.test.ts packages/app/src/cli/services/app-doctor-instructions.test.ts packages/app/src/cli/services/app-doctor-api.test.ts
pnpm --filter @shopify/app type-check
pnpm --filter @shopify/app lint

Post-release steps

After #8495 merges, rebase this branch onto updated main and regenerate packages/app/src/cli/services/app-doctor-engine/checks/embedded.ts before merging so the generated prompt bundle and check counts reflect both PRs.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add