Migrate away from the embedded Express server, embrace pure Vite plugins implementation

This should not be too difficult, but that will make Gracile a bit less personalized regarding dev/build lifecycle. Some of the benefits are : - User can "augment" an existing Vite project with Gracile - It's becoming a pattern, since Remix opted for this approach - That will shrink deps. by a good bit. Express is definitely too heavy with a deep dep-tree. - Internal sources will be fairly simplified. - Some CLI entrypoint will become obsolete - Tests should be more stable. For now, Gracile runtime can be fiddly to start/stop, especially when a crash occurs (stuck) Custom CLI entrypoint will have to be preserved for launching the Vite Runtime when using the `server` output with user provided server instance (loadable from a file entrypoint option, still undocumented).