Dev mode auto-restart too aggressive: restarts on any file change including build artifacts

## Problem

Dev mode watches component directories and restarts on any file change — including files written by the component itself during normal operation (e.g., Next.js writes to `.next/` on build, which triggers a restart, which triggers a build, creating an infinite loop).

## Fix

Restarts from `watchDir` should only fire when `restartRequired` is signaled by the component plugin API — not for every file change. When a plugin can handle a change dynamically (e.g., `static`), no restart should occur.

For built-in components that don't yet implement the plugin API, implement it so they can signal `restartRequired` appropriately rather than using the blanket file-change trigger.

🤖 Filed by Claude on behalf of Kris.