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)

backend/toolbox/workflows/android_static_analysis/activities.py

@@ -112,10 +112,23 @@ async def scan_with_mobsf_activity(workspace_path: str, config: dict) -> dict:
         config: MobSFScanner configuration
 
     Returns:
-        Scan results dictionary
+        Scan results dictionary (or skipped status if MobSF unavailable)
     """
     logger.info(f"Activity: scan_with_mobsf (workspace={workspace_path})")
 
+    # Check if MobSF is installed (graceful degradation for ARM64 platform)
+    mobsf_path = Path("/app/mobsf")
+    if not mobsf_path.exists():
+        logger.warning("MobSF not installed on this platform (ARM64/Rosetta limitation)")
+        return {
+            "status": "skipped",
+            "findings": [],
+            "summary": {
+                "total_findings": 0,
+                "skip_reason": "MobSF unavailable on ARM64 platform (Rosetta 2 incompatibility)"
+            }
+        }
+
     try:
         from modules.android import MobSFScanner
 

backend/toolbox/workflows/android_static_analysis/workflow.py

@@ -196,9 +196,16 @@ class AndroidStaticAnalysisWorkflow:
                         maximum_attempts=2  # MobSF can be flaky, limit retries
                     ),
                 )
-                workflow.logger.info(
-                    f"✓ MobSF completed: {mobsf_result.get('summary', {}).get('total_findings', 0)} findings"
-                )
+
+                # Handle skipped or completed status
+                if mobsf_result.get("status") == "skipped":
+                    workflow.logger.warning(
+                        f"⚠️  MobSF skipped: {mobsf_result.get('summary', {}).get('skip_reason', 'Unknown reason')}"
+                    )
+                else:
+                    workflow.logger.info(
+                        f"✓ MobSF completed: {mobsf_result.get('summary', {}).get('total_findings', 0)} findings"
+                    )
             except Exception as e:
                 workflow.logger.warning(f"MobSF scan failed (continuing without it): {e}")
                 mobsf_result = None