web_ui: support unix:<path> upstreams in extraWebProxies

reqwest has no UDS transport, so unix: upstreams dial the socket
directly with a raw hyper/1.1 client per request instead. http(s)://
upstreams are unaffected (still go through the existing reqwest path).

Adds hyper (client, http1), hyper-util (tokio IO adapter), and
http-body-util as direct hive-ag3nt dependencies - all three were
already present transitively via reqwest, this just uses them
directly for the new code path.

Cargo.toml

@@ -68,6 +68,9 @@ reqwest = { version = "0.12", default-features = false, features = [
   "json",
   "rustls-tls",
 ] }
+hyper = { version = "1", features = ["client", "http1"] }
+hyper-util = { version = "0.1", features = ["tokio"] }
+http-body-util = "0.1"
 forgejo-api = { version = "0.11", default-features = false, features = [
   "rustls-tls",
 ] }