Fix Mixpanel analytics review findings FRE-5281

P0: Fix validation bypass - validated properties now override raw properties
P1: Add unit tests for shared-analytics package (3 test files)
P1: Refactor spamshield to use shared-analytics, deprecate duplicate
P2: Normalize phone numbers to E.164 before hashing
P2: Add graceful error handling for missing env vars in config
P3: Add singleton pattern to MixpanelService
P3: Include timestamp in validated properties schema

services/spamshield/package.json

@@ -12,6 +12,7 @@
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
+    "@shieldsai/shared-analytics": "workspace:*",
     "@shieldai/db": "workspace:*",
     "@shieldai/types": "workspace:*",
     "@shieldai/correlation": "workspace:*",