Add AI agent decision memory layer with pgvector similarity search

- models/agentdecision.go: AgentDecision GORM model (context/decision as jsonb, reasoning as text)
- migrations/migrate.go: AutoMigrate AgentDecision then ALTER TABLE to add vector(1536) column and CREATE ivfflat index via raw SQL
- controllers/agentDecisionController.go: CreateAgentDecision, FindSimilarDecisions (cosine distance), UpdateDecisionOutcome
- routes/routes.go: three routes under /api/v1/internal (InternalKeyAuth applied at group level)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

migrations/migrate.go

@@ -40,6 +40,7 @@ func Migrate(db *gorm.DB) error {
 		&models.CompetitorBranch{},
 		&models.CarrierPricing{},
 		&models.DoormilePricing{},
+		&models.AgentDecision{},
 	)
 
 	if err != nil {
@@ -48,5 +49,18 @@ func Migrate(db *gorm.DB) error {
 	}
 
 	utils.Info("✅ Database migration completed successfully!")
+
+	if res := db.Exec(`ALTER TABLE agent_decisions ADD COLUMN IF NOT EXISTS context_embedding vector(1536)`); res.Error != nil {
+		utils.Error("❌ Failed to add context_embedding column", "error", res.Error)
+	} else {
+		utils.Info("✅ context_embedding vector column ready")
+	}
+
+	if res := db.Exec(`CREATE INDEX IF NOT EXISTS idx_agent_decisions_embedding ON agent_decisions USING ivfflat (context_embedding vector_cosine_ops) WITH (lists = 100)`); res.Error != nil {
+		utils.Error("❌ Failed to create ivfflat index on context_embedding", "error", res.Error)
+	} else {
+		utils.Info("✅ ivfflat index on context_embedding ready")
+	}
+
 	return nil
 }