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/gormlog/gormlog.go

@@ -7,7 +7,7 @@
 // SQL — parameters and all — for every statement that returns an
 // error, including gorm.ErrRecordNotFound. Two of this service's
 // lookups miss by design on unauthenticated routes: the entrypoint
-// lookup on /webhook/{uuid}, whose path segment the client picks
+// lookup on /h/{uuid}, whose path segment the client picks
 // outright, and the user lookup behind the login form, whose username
 // the client picks outright. Under the default logger each of those
 // misses printed an unbounded, attacker-chosen string, at no level the