codeSplitter: dependency doctor, the self-building dependency system (epic) #859

The dependency doctor (apps/codesplitter/src/deps.ts) already proposes updates on a schedule, waits out a minimum release age, tests in a throwaway clone, hands breakage to an AI fixer, and bumps vulnerable versions via OSV. This epic makes it the self-building dependency system for a repo: Dependabot/Renovate-style updates with no per-repo CI setup, an owner-controlled response when something fails, and checks that go through the real provision → deploy → teardown loop.

Pieces:

• codeSplitter: Dependency doctor: repo health page, your versions vs latest #860 Dependency doctor: repo health page, your versions vs latest
• codeSplitter: Dependency doctor: owner-built on-fail chain (retry, AI fix, web search, hold, roll back, alert) #861 Dependency doctor: owner-built on-fail chain (retry, AI fix, web search, hold, roll back, alert) (codeSplitter dependency doctor: owner-built on-fail chain (retry, AI fix, web search, hold, roll back, alert) #869)
• codeSplitter: Dependency doctor: rank the packages you care about to settle conflicts #862 Dependency doctor: rank the packages you care about to settle conflicts (PR codeSplitter dependency doctor: rank the packages you care about to settle clashes (#862) #886)
• codeSplitter: Dependency doctor: 🪏 dig a future release to watch, try, and take #863 Dependency doctor: 🪏 dig a future release to watch, try, and take (PR codeSplitter dependency doctor: 🪏 dig a future release to watch, try, and take (#863) #884)
• codeSplitter: Dependency doctor: verify updates with a preview deploy, then tear down #864 Dependency doctor: verify updates with a preview deploy, then tear down