turbo-wiki: add --serve mode with live page updates
Serves the wiki from the latest settled snapshot in memory and streams
changed page names to open tabs over server-sent events; a small injected
script refetches the current page and patches the document in place. The
compilation is the same standing root-task query as --watch, just with an
HTTP consumer instead of a directory writer. Hand-rolled HTTP/SSE to keep
the crate dependency-free.