refactor: Implement 2-container architecture to solve USB stability issues

BREAKING CHANGE: Switched from single-container to multi-container setup

This commit introduces a meshcore-bridge service that isolates USB device
access from the main application, resolving persistent USB timeout and
deadlock issues in Docker + VM environments.

Changes:
- Add meshcore-bridge/ - Lightweight HTTP API wrapper for meshcli
  - Flask server exposes /cli endpoint (port 5001, internal only)
  - Exclusive USB device access via --device flag
  - Health check endpoint at /health

- Refactor app/meshcore/cli.py
  - Replace subprocess calls with HTTP requests to bridge
  - Add requests library dependency
  - Better error handling for bridge communication

- Update docker-compose.yml
  - Define meshcore-bridge and mc-webui services
  - Create meshcore-net Docker network
  - Add depends_on with health check condition
  - Bridge gets USB device, main app uses HTTP only

- Modify Dockerfile
  - Remove meshcore-cli installation from main app
  - Lighter image without gcc dependencies

- Update config.py
  - Add MC_BRIDGE_URL environment variable
  - Remove meshcli_command property (no longer needed)

- Update documentation (README.md, .claude/instructions.md)
  - Document 2-container architecture
  - Add troubleshooting section for bridge
  - Update prerequisites (no host meshcore-cli needed)
  - Add architecture diagram in project structure

Benefits:
✅ Solves USB device locking after container restarts
✅ Restartable main app without USB reset
✅ Better separation of concerns
✅ Easier debugging (isolated meshcli logs)
✅ No manual USB recovery scripts needed

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

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

Dockerfile

@@ -1,25 +1,17 @@
 # mc-webui Dockerfile
-# Python 3.11+ with Flask and meshcore-cli
+# Python 3.11+ with Flask (meshcore-cli runs in separate bridge container)
 
 FROM python:3.11-slim
 
 # Set working directory
 WORKDIR /app
 
-# Install system dependencies
-RUN apt-get update && apt-get install -y \
-    gcc \
-    && rm -rf /var/lib/apt/lists/*
-
 # Copy requirements first for better layer caching
 COPY requirements.txt .
 
 # Install Python dependencies
 RUN pip install --no-cache-dir -r requirements.txt
 
-# Install meshcore-cli
-RUN pip install --no-cache-dir meshcore-cli
-
 # Copy application code
 COPY app/ ./app/