feat: Major UI improvements and SSH-only mode

- Tool rendering: Unified tool_use/tool_result cards with collapsible results
- Special rendering for WebSearch, WebFetch, Task, Write tools
- File upload support with drag & drop
- Permission dialog for tool approvals
- Status bar with session stats and permission mode toggle
- SSH-only mode: Removed local container execution
- Host switching disabled during active session with visual indicator
- Directory browser: Browse remote directories via SSH
- Recent directories dropdown with localStorage persistence
- Follow-up messages during generation
- Improved scroll behavior with "back to bottom" button

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

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

frontend/Dockerfile

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1.4
 # Build stage
 FROM node:20-slim AS builder
 
@@ -14,8 +15,9 @@ ENV VITE_API_URL=$VITE_API_URL
 # Copy package files
 COPY package*.json ./
 
-# Install dependencies
-RUN npm install
+# Install dependencies with cache mount
+RUN --mount=type=cache,target=/root/.npm \
+    npm install
 
 # Copy source
 COPY . .