feat: replace runtime ubuntu image with custom snek_ubuntu and move r binary into Dockerfile

Add DockerfileUbuntu that pre-installs r binary and all required system dependencies, removing the need for per-container apt installs and binary copy from .bashrc. Update terminal view to use the new snek_ubuntu image instead of ubuntu:latest. Fix terminal session buffer check to use self.history instead of self.buffer. Add docker build target to Makefile.

src/snek/system/terminal.py

@@ -32,7 +32,7 @@ class TerminalSession:
 
     async def read_output(self, ws):
         self.sockets.append(ws)
-        if len(self.sockets) > 1 and self.buffer:
+        if len(self.sockets) > 1 and self.history:
             start = 0
             try:
                 start = self.history.index(b'\n')

src/snek/view/terminal.py

@@ -30,7 +30,10 @@ class TerminalSocketView(BaseView):
         user = await self.services.user.get(uid=self.session.get("uid"))
         root = await self.prepare_drive()
         
-        command = f"docker run -v ./{root}/:/root --rm -it --memory 512M --cpus=0.5 -w /root ubuntu:latest /bin/bash"
+
+        
+
+        command = f"docker run -v ./{root}/:/root -it --memory 512M --cpus=0.5 -w /root snek_ubuntu /bin/bash"
 
         session = self.user_sessions.get(user["uid"])
         if not session: