Migrate burden-forecast fan-out from isRegistered to isInstalled

[JSONbored]

Part of #5016. Depends on #5028 (isInstalled reliability).

Problem

buildBurdenForecasts (src/queue/processors.ts:4588-4595) fans out queue-burden forecasting per isRegistered repo — same shape as #1 (signal snapshots), and equally unrelated to subnet economics: general repo-health forecasting that any self-host operator's installed repos should get.

Target

Change the filter from isRegistered to isInstalled.

Requirements

• Same shape as feat(docs): add install site and mcp diagnostics #1/chore(release): prepare public gittensory launch #2: installed-not-registered repos included, registered-not-installed repos excluded.

Deliverables

• Updated filter.
• Regression test mirroring feat(docs): add install site and mcp diagnostics #1/chore(release): prepare public gittensory launch #2's pattern.
• Full local gate green, 99% patch coverage on the diff.

[linear-code]

JSO-3632