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>

routes/routes.go

@@ -274,6 +274,9 @@ func RegisterRoutes(app *fiber.App, cfg *config.Config) {
 	internal := api.Group("/internal", middlewares.InternalKeyAuth)
 	internal.Post("/notify", controllers.InternalNotify)
 	internal.Post("/bookings/:id/reassign", controllers.InternalReassign)
+	internal.Post("/agent-decisions", controllers.CreateAgentDecision)
+	internal.Get("/agent-decisions/similar", controllers.FindSimilarDecisions)
+	internal.Patch("/agent-decisions/:id/outcome", controllers.UpdateDecisionOutcome)
 
 	// --------------------
 	// WEBSOCKET — live miler tracking (no auth, public tracking link)