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/hooks/useClaudeSession.js

@@ -203,14 +203,15 @@ export function useClaudeSession() {
     }
   }, []);
 
-  const loadHistory = useCallback(async (project) => {
+  const loadHistory = useCallback(async (project, host = null) => {
     try {
       const encodedProject = encodeURIComponent(project);
-      const response = await fetch(`${API_URL}/api/history/${encodedProject}`);
+      const hostParam = host ? `?host=${host}` : '';
+      const response = await fetch(`${API_URL}/api/history/${encodedProject}${hostParam}`);
       if (response.ok) {
         const data = await response.json();
         if (data.messages && data.messages.length > 0) {
-          console.log(`Loaded ${data.messages.length} messages from history`);
+          console.log(`Loaded ${data.messages.length} messages from history (source: ${data.source || 'local'})`);
           setMessages(data.messages);
           return data.sessionId;
         }
@@ -221,7 +222,7 @@ export function useClaudeSession() {
     return null;
   }, []);
 
-  const startSession = useCallback(async (project = '/projects', resume = true) => {
+  const startSession = useCallback(async (project = '/projects', resume = true, host = null) => {
     if (!wsRef.current || wsRef.current.readyState !== WebSocket.OPEN) {
       setError('Not connected');
       return;
@@ -229,13 +230,14 @@ export function useClaudeSession() {
 
     // Load history before starting session if resuming
     if (resume) {
-      await loadHistory(project);
+      await loadHistory(project, host);
     }
 
     wsRef.current.send(JSON.stringify({
       type: 'start_session',
       project,
-      resume
+      resume,
+      host
     }));
   }, [loadHistory]);