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. Route tests reach every moved page and form through the
production router, taking each URL and token from the rendered page.

Model: opus-5-5

internal/handlers/target_create_query_test.go

@@ -76,11 +76,11 @@ func postTargetCreate(
 	router := chi.NewRouter()
 	router.Use(mw.Logging())
 	router.Post(
-		"/source/{sourceID}/targets",
+		"/hook/{sourceID}/targets",
 		env.handlers.HandleTargetCreate(),
 	)
 
-	target := "/source/" + webhookID + "/targets"
+	target := "/hook/" + webhookID + "/targets"
 	if query != "" {
 		target += "?" + query
 	}
@@ -114,7 +114,7 @@ func postTargetCreate(
 // regression test for the ingress leak. r.FormValue falls back to the
 // query string when a field is absent from the POST body, so
 //
-//	POST /source/{id}/targets?url=https://hooks.slack.com/services/...
+//	POST /hook/{id}/targets?url=https://hooks.slack.com/services/...
 //
 // with an empty url field used to create a working target from a value
 // carried on the request line — where logs, proxies, Referer headers