FRE-4510: Implement feature flag checks for spam classification

- Add runtime flag evaluation from FLAG_<KEY> environment variables
- Add enableCallAnalysis flag check to analyzeCall() and interceptCall()
- Add enableFeedbackLoop flag check to recordFeedback()
- Add 19 tests for feature flag behavior (checkFeatureFlag, getters, service integration)
- Add vitest config and test script to spamshield package

services/spamshield/src/config/spamshield.config.ts

@@ -4,7 +4,7 @@ export const spamRateLimits = {
   PREMIUM: 2000,
 } as const;
 
-export const spamFeatureFlags = {
+export const spamFeatureFlagDefaults = {
   enableHiyaIntegration: true,
   enableTruecallerIntegration: true,
   enableSMSClassification: true,
@@ -12,11 +12,42 @@ export const spamFeatureFlags = {
   enableFeedbackLoop: true,
 } as const;
 
+type FeatureFlagKey = keyof typeof spamFeatureFlagDefaults;
+
+export function checkFeatureFlag(flag: FeatureFlagKey): boolean {
+  const envKey = `FLAG_${flag.toUpperCase()}`;
+  const envValue = process.env[envKey];
+
+  if (envValue !== undefined) {
+    return envValue === 'true' || envValue === '1';
+  }
+
+  return spamFeatureFlagDefaults[flag];
+}
+
+export const spamFeatureFlags = {
+  get enableHiyaIntegration() {
+    return checkFeatureFlag('enableHiyaIntegration');
+  },
+  get enableTruecallerIntegration() {
+    return checkFeatureFlag('enableTruecallerIntegration');
+  },
+  get enableSMSClassification() {
+    return checkFeatureFlag('enableSMSClassification');
+  },
+  get enableCallAnalysis() {
+    return checkFeatureFlag('enableCallAnalysis');
+  },
+  get enableFeedbackLoop() {
+    return checkFeatureFlag('enableFeedbackLoop');
+  },
+} as const;
+
 export const spamConfig = {
   maxPhoneNumberLength: 20,
   minPhoneNumberLength: 10,
   defaultConfidenceThreshold: 0.7,
-  maxMetadataSize: 1024 * 10, // 10KB
+  maxMetadataSize: 1024 * 10,
   circuitBreakerThreshold: 5,
   circuitBreakerTimeout: 60000,
 } as const;