chore(mapgen-studio): simplify dev host process

[mateicanavra]

The dev script now runs the daemon and Vite frontend in a single Bun process rather than spawning them as separate child processes. bun --watch is added to the dev script so that Bun's file watcher owns backend restarts via the devLive.ts entrypoint, while Vite continues to handle frontend HMR. Vite is started in-process using createServer from the Vite API instead of being spawned as a subprocess.

The DevLivePlan type is updated to reflect this: the daemon and vite fields now describe configuration values (host, port, config file path) rather than subprocess commands and arguments. The DevLiveCommand and RunningChild types are removed entirely, along with the startChild and waitForFirstExit helpers. Signal handling is updated to cleanly shut down the in-process Vite server and daemon on SIGINT/SIGTERM and exit with the appropriate code.

The runbook is updated to document the direct watcher invocation (bun --watch src/server/daemon/devLive.ts) as the preferred command for detached local sessions where dependencies are already prepared.

[mateicanavra]

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• chore(mapgen-studio): simplify dev host process #1699 👈 (View in Graphite)
• fix(mapgen-studio): launch selected map in game #1698
• chore: add .nx/ to .gitignore #1697
• feat(studio-server): replay latest live-game event to late watch subscribers #1696
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