cli player agent added

ARCHITECTURE.md

@@ -44,7 +44,9 @@ flowchart TB
     Audio[racket-audio<br/>local backend]
     Discovery[racket-upnp + racket-sonos<br/>device discovery]
     DLNA[racket-audio-dlna<br/>network backend and media server]
-    Agent[player-agent.rkt<br/>polling Windows renderer]
+    AgentGUI[private/player-agent-gui.rkt<br/>GUI adapter]
+    AgentCLI[player-agent-cli.rkt<br/>CLI adapter]
+    AgentCore[private/player-agent-core.rkt<br/>polling and audio runtime]
 
     Main --> Server
     Main --> Player
@@ -56,8 +58,10 @@ flowchart TB
     Player --> Audio
     Player --> Discovery
     Player --> DLNA
-    Agent --> Server
-    Agent --> Audio
+    AgentGUI --> AgentCore
+    AgentCLI --> AgentCore
+    AgentCore --> Server
+    AgentCore --> Audio
 ```
 
 ### 3.1 Entrypoint and lifecycle
@@ -327,6 +331,11 @@ INI allowlist. Media URLs additionally contain an opaque per-track token. The
 random application ID therefore acts as a shared bearer credential, but must
 not be treated as strong authentication when transported over unencrypted HTTP.
 
+The GUI and CLI playback agents share one headless runtime. The GUI only adapts
+configuration and state to widgets. Optional tray integration is loaded
+dynamically through SDL3, so CLI use and the default GUI installation do not
+acquire a mandatory SDL dependency.
+
 The configured library roots define the intended filesystem boundary. Clients
 operate on opaque indexes instead of sending paths directly. The DLNA backend
 must make a selected local file reachable by the network renderer, so its media