feat: add platform-aware worker architecture with ARM64 support

Implement platform-specific Dockerfile selection and graceful tool degradation to support both x86_64 and ARM64 (Apple Silicon) platforms.

**Backend Changes:**
- Add system info API endpoint (/system/info) exposing host filesystem paths
- Add FUZZFORGE_HOST_ROOT environment variable to backend service
- Add graceful degradation in MobSF activity for ARM64 platforms

**CLI Changes:**
- Implement multi-strategy path resolution (backend API, .fuzzforge marker, env var)
- Add platform detection (linux/amd64 vs linux/arm64)
- Add worker metadata.yaml reading for platform capabilities
- Auto-select appropriate Dockerfile based on detected platform
- Pass platform-specific env vars to docker-compose

**Worker Changes:**
- Create workers/android/metadata.yaml defining platform capabilities
- Rename Dockerfile -> Dockerfile.amd64 (full toolchain with MobSF)
- Create Dockerfile.arm64 (excludes MobSF due to Rosetta 2 incompatibility)
- Update docker-compose.yml to use ${ANDROID_DOCKERFILE} variable

**Workflow Changes:**
- Handle MobSF "skipped" status gracefully in workflow
- Log clear warnings when tools are unavailable on platform

**Key Features:**
- Automatic platform detection and Dockerfile selection
- Graceful degradation when tools unavailable (MobSF on ARM64)
- Works from any directory (backend API provides paths)
- Manual override via environment variables
- Clear user feedback about platform and selected Dockerfile

**Benefits:**
- Android workflow now works on Apple Silicon Macs
- No code changes needed for other workflows
- Convention established for future platform-specific workers

Closes: MobSF Rosetta 2 incompatibility issue
Implements: Platform-aware worker architecture (Option B)

docker-compose.yml

@@ -342,7 +342,7 @@ services:
   worker-android:
     build:
       context: ./workers/android
-      dockerfile: Dockerfile
+      dockerfile: ${ANDROID_DOCKERFILE:-Dockerfile.amd64}
     container_name: fuzzforge-worker-android
     profiles:
       - workers
@@ -430,6 +430,9 @@ services:
       PYTHONPATH: /app
       PYTHONUNBUFFERED: 1
 
+      # Host filesystem paths (for CLI worker management)
+      FUZZFORGE_HOST_ROOT: ${PWD}
+
       # Logging
       LOG_LEVEL: INFO
     ports: