feat(proxy): accept transparent redirected connections

The proxy only accepted explicit clients, which announce their
destination with a CONNECT request. A client whose connection is
redirected at the kernel level speaks TLS immediately instead, so
http.Server tries to parse a TLS record as an HTTP request line and
drops the connection.

Demultiplex on the first byte of an accepted connection. A TLS
handshake record (0x16) cannot begin an HTTP method, so it separates
the two cleanly. Redirected connections have their destination
recovered from the ClientHello SNI and are served by synthesising the
CONNECT the client never sent, which keeps the MITM decision, cert
generation and interceptor chain on the existing code path.

Redirected connections deliberately bypass http.Server. It issues a
background read while a handler runs, which consumes the first byte of
the replayed ClientHello and corrupts the handshake. The CONNECT
response is also suppressed, since a client mid handshake expects a
ServerHello and would read those bytes as a malformed TLS record.

Off by default. Enabled with `pmg proxy start --transparent` or
proxy.server.transparent, and only useful alongside a redirect
mechanism such as an eBPF connect rewrite.

config/config.go

@@ -181,6 +181,14 @@ type ProxyServerConfig struct {
 	// ListenPort is the port the persistent proxy binds to. 0 (default) means a
 	// random free port. The --port flag overrides this.
 	ListenPort int `mapstructure:"listen_port"`
+
+	// Transparent additionally accepts connections that were redirected to the
+	// proxy rather than addressed to it. A redirected client believes it reached
+	// the real registry, so it speaks TLS immediately instead of sending CONNECT,
+	// and its destination is recovered from the TLS SNI. Off by default: it is
+	// only useful alongside a redirect mechanism such as the Linux eBPF
+	// enforcement layer. The --transparent flag overrides this.
+	Transparent bool `mapstructure:"transparent"`
 }
 
 // SandboxConfig configures the sandbox system for isolating package manager processes.