Patch existing projects' seeded worker.ts (template fixes only reach new projects)

Every project repo carries its own frozen copy of the seeded configs/default/worker.ts; template fixes only apply to projects created after the fix ships. Known drift in old copies:

• Stub-disposal leak (#1845 follow-up): the agent-birth reaction drops its env.ITX.get() root stub, so every agent birth in an OLD project emits one workerd "An RPC stub was not disposed properly" warning into prd observability logs. New projects release the stub via try/finally (guarded — a throwing dispose after the append would double-apply birth defaults on redelivery, since those events carry no idempotency key by design per #1831).
• Whatever else has accumulated since each project's creation (this stacks on the older "patch old prd repos' worker.ts" note from the userspace project processor work, #1761/#1778).

Approach sketch: a one-shot admin script that walks projects, diffs their worker.ts against the current template, and commits the delta where the file is unmodified from ITS seeded version (projects that customized their worker need a human or an agent to merge). The warning is benign noise, not breakage — prioritize accordingly.