Move webhook pages to /hook/ID and inbound URLs to /h/UUID (closes #367)

The webhook page and everything under it move from /source/ID to /hook/ID; the list and new-webhook form from /sources to /hooks and /hooks/new; the event log from .../logs to /hook/ID/events; entrypoint URLs, the ones senders post to, from /webhook/UUID to /h/UUID. The old paths are simply gone, per the owner's ruling. Every link, redirect, form action, test, comment and README mention follows; every link to the event log, and its title and heading, read "Full Event Log".

Keeping the UUID out of logs, metrics labels and error reports, and the receiver rate limits, key on the route itself, so they cover /h/ unchanged. Routed tests follow every link and form the pages render to a moved page.

Model: opus-5-5

internal/middleware/middleware.go

@@ -257,7 +257,7 @@ func concreteLogURL(r *http.Request) string {
 //
 // 3xx and 4xx responses get the chi route pattern instead. Those are
 // the outcomes an unauthenticated client drives for free: 404 or 429
-// on any invented /webhook/ path, 303 to the login page on any
+// on any invented /h/ path, 303 to the login page on any
 // invented /user/ path. Logging the concrete URL there lets a flood
 // write attacker-chosen text, of attacker-chosen length, into the
 // operator's log at one line per request. The pattern comes from the
@@ -560,7 +560,7 @@ func (s *Middleware) MaxBodySize(
 				// internal/server/routes.go), so an
 				// unauthenticated client reaches it with a path
 				// of its own choosing and its own length —
-				// POST /source/<8 KB>/edit with an oversize
+				// POST /hook/<8 KB>/edit with an oversize
 				// declared Content-Length costs nothing to
 				// send. At WARN, on by default, that is a
 				// write into the operator's log sized by the