feat: Add SSH remote execution for multi-host Claude sessions

- Backend: SSH execution via spawn() with -T flag for JSON streaming
- Backend: PATH setup for non-login shells on remote hosts
- Backend: History loading via SSH (tail -n 2000 for large files)
- Frontend: Host selector UI with colored buttons in Sidebar
- Frontend: Auto-select first project when host changes
- Frontend: Pass host parameter to history and session APIs
- Docker: Install openssh-client, mount SSH keys

Enables running Claude sessions on remote hosts via SSH while
viewing them through the web UI.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/App.jsx

@@ -101,6 +101,7 @@ function App() {
   } = useClaudeSession();
 
   const [selectedProject, setSelectedProject] = useState('/projects/claude-web-ui');
+  const [selectedHost, setSelectedHost] = useState('local');
   const [sidebarOpen, setSidebarOpen] = useState(true);
   const [resumeSession, setResumeSession] = useState(true);
 
@@ -114,7 +115,7 @@ function App() {
   }, [setMessages]);
 
   const handleStartSession = () => {
-    startSession(selectedProject, resumeSession);
+    startSession(selectedProject, resumeSession, selectedHost);
   };
 
   // Handle slash commands
@@ -167,6 +168,8 @@ function App() {
         onToggle={() => setSidebarOpen(!sidebarOpen)}
         selectedProject={selectedProject}
         onSelectProject={setSelectedProject}
+        selectedHost={selectedHost}
+        onSelectHost={setSelectedHost}
         sessionActive={sessionActive}
         onStartSession={handleStartSession}
         onStopSession={stopSession}