Update Python version requirements and fix compatibility issues

- Bump minimum Python version from 3.11 to 3.13 across all apps
- Add Python 3.11-3.13 test matrix to CLI workflow
- Document Python 3.11+ requirement in .env.example
- Fix Starlette Broadcast removal with in-process fallback implementation
- Add _InProcessBroadcast class for tests when Starlette Broadcast is unavailable
- Refactor API key validators to read live settings instead of cached values
- Update database models with explicit

apps/zk-circuits/ml_inference_verification.circom

@@ -0,0 +1,26 @@
+pragma circom 2.0.0;
+
+// Simple ML inference verification circuit
+// Basic test circuit to verify compilation
+
+template SimpleInference() {
+    signal input x;     // input
+    signal input w;     // weight
+    signal input b;     // bias
+    signal input expected; // expected output
+
+    signal output verified;
+
+    // Simple computation: output = x * w + b
+    signal computed;
+    computed <== x * w + b;
+
+    // Check if computed equals expected
+    signal diff;
+    diff <== computed - expected;
+
+    // Use a simple comparison (0 if equal, non-zero if different)
+    verified <== 1 - (diff * diff);  // Will be 1 if diff == 0, 0 otherwise
+}
+
+component main = SimpleInference();