Desktop E2E fixtures no longer seed Runtime Host connections #2704

What happened

After #2700 removed the legacy Runtime Policy migration, the shared Desktop Playwright fixture still seeds llm-connections.json and the legacy credential store. The Desktop E2E Runtime Host candidate disables automatic policy bootstrap, so its authoritative catalog is empty. Onboarding hides the composer and 16 of 17 E2E tests time out before reaching their assertions.

Expected: seedE2eConnection should populate the current Runtime Host connection catalog, credential vault, model inventory, and default target before Electron launches.

How to reproduce

1. Check out current main at 94e677579.
2. Run npm ci.
3. Run npm --workspace @maka/desktop run e2e.
4. Observe 16 seeded tests time out waiting for the visible composer; the only seed: false artifact fixture passes.

Environment

• Maka commit: 94e677579
• OS: reproduced on macOS; the hosted Linux E2E job shows the same fixture timeout
• Surface: Desktop E2E / Runtime Host
• Node.js: repository-supported Node 22+

Additional context

The production migration should remain removed. The fixture should acquire the interactive root owner, seed through openInteractiveRuntimePolicyStoresForWrite, release the owner before launching Electron, and keep the fake backend for actual test sessions.

I am working on the fixture-only fix and regression coverage.