fix(caddy): tell Audiobookshelf its real scheme so the OIDC callback validates

ABS checks every OIDC callback against the origin it believes it is served from:
getRequestOrigin() is x-forwarded-proto://Host (dist-server/server/utils/requestUtils.js,
read in the pinned image digest 2026-11-03). The post-auth http://:8017 listener is fed
over plain http, so Caddy's own X-Forwarded-Proto is http, ABS derives
http://abs.franksdank.cloud, and answers its own https callback with

    400 {"message":"Invalid callback URL - must be same-origin"}

Measured at the app with the callback held fixed: Host abs.franksdank.cloud alone
reproduces the 400 (as does every other Host, including the bare LAN IP), and adding
`X-Forwarded-Proto: https` turns it into a 302 to /application/o/authorize/ carrying
the registered redirect_uri. The edge for a guarded name is TLS-only, so https is the
truthful value, not a spoof; the LAN door needs nothing because there browser and
server already agree on http, which is why only the guarded path was broken.

dankclaw/Caddyfile

@@ -429,7 +429,16 @@ http://:8017 {
 		# convenience hop, taken post-auth so nothing reaches the app
 		# pre-authentication.
 		redir / /audiobookshelf/ permanent
-		reverse_proxy 192.168.0.235:8000
+		# Audiobookshelf validates every OIDC callback against the origin it
+		# believes it is served from — getRequestOrigin() is
+		# x-forwarded-proto://Host — and a mismatch is a bodiless 400
+		# "Invalid callback URL - must be same-origin" before the IdP is ever
+		# contacted (measured 2026-11-03). This listener is fed over plain http
+		# by the outpost, so Caddy's own X-Forwarded-Proto here says http; the
+		# edge for this name is TLS-only, so https is the truthful value.
+		reverse_proxy 192.168.0.235:8000 {
+			header_up X-Forwarded-Proto https
+		}
 	}
 
 	@prowlarr host prowlarr.franksdank.cloud