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 to /hooks and /hooks/new, and
the event log from .../logs to /hook/ID/events, body download
included. Entrypoint URLs move from /webhook/UUID to /h/UUID, and the
webhook page shows only that form. The old paths are gone.

Links, redirects, form actions, tests, comments and the README follow.
Both links to the event log page, and its title and heading, now read
"Full Event Log". Go identifiers and template file names are
unchanged. A new route test posts to the entrypoint URL the webhook
page shows and checks that the receiver rate limit applies to it.

Model: opus-5-5

internal/middleware/metrics_method_test.go

@@ -50,7 +50,7 @@ func realMethods() []string {
 // dimension varying, so any series growth a probe produces is the
 // method label's and nothing else's.
 func methodProbePath() string {
-	return "/webhook/" + uuid.NewString()
+	return "/h/" + uuid.NewString()
 }
 
 // inventedMethods returns n distinct RFC 9110 method tokens that no