FRE-4518: Replace hardcoded default score values with constants

- Created decision-engine.constants.ts with all scoring weights, thresholds, and behavioral scores
- Updated decision-engine.ts to import and use constants instead of inline values
- All 12 hardcoded values now have named, documented constants
- Pre-existing type errors are unrelated to this change

services/spamshield/src/constants/decision-engine.constants.ts

@@ -0,0 +1,27 @@
+/**
+ * Decision Engine Constants
+ * 
+ * Scoring weights, thresholds, and behavioral factors used in spam detection.
+ * These values should be reviewed periodically and updated based on model performance.
+ */
+
+/** Scoring Weights */
+export const DEFAULT_REPUTATION_WEIGHT = 0.4;
+export const DEFAULT_RULE_WEIGHT = 0.3;
+export const DEFAULT_BEHAVIORAL_WEIGHT = 0.2;
+export const DEFAULT_USER_HISTORY_WEIGHT = 0.1;
+
+/** Decision Thresholds */
+export const DEFAULT_BLOCK_THRESHOLD = 0.85;
+export const DEFAULT_FLAG_THRESHOLD = 0.60;
+
+/** Behavioral Analysis Scores */
+export const SHORT_CALL_SCORE = 0.3;      // Call duration < 5 seconds
+export const SHORT_SMS_SCORE = 0.1;       // SMS call type
+export const SHORT_CONTENT_SCORE = 0.2;   // SMS body < 10 characters
+export const URGENT_KEYWORD_SCORE = 0.3;  // Contains urgent/act now/limited keywords
+
+/** Default Fallback Values */
+export const DEFAULT_EVALUATION_TIMEOUT = 200; // milliseconds
+export const DEFAULT_FALLBACK_DECISION = 'ALLOW';
+export const DEFAULT_FALLBACK_ON_TIMEOUT = true;