refactor: simplify crud-pricing to pure CRUD layer - remove AWS API clients

Removed AWS Pricing API and Cost Explorer clients to make crud-pricing
a pure DynamoDB CRUD layer. This fixes layer violation where CRUD was
making external AWS API calls.

Changes:
- Deleted src/aws_pricing.rs (AWS Pricing API client)
- Deleted src/cost_explorer.rs (Cost Explorer client)
- Removed PricingClient and StsClient from main.rs
- Removed QueryAwsApi and QueryCostExplorer operations
- Removed fetch_if_missing behavior (Get operation now only reads from cache)
- Removed aws-sdk-pricing, aws-sdk-costexplorer, aws-sdk-sts dependencies
- Removed pricing_api_access and sts_assume_role IAM policies

Result: Pure CRUD layer with only DynamoDB operations (Get, Put, ListCommon, IncrementAccess)
Reduced from ~1100 lines to ~600 lines

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

terraform/main.tf

@@ -23,6 +23,11 @@ provider "aws" {
   }
 }
 
+# Data source: Get Gateway ID from platform-core
+data "aws_ssm_parameter" "gateway_id" {
+  name = "/airun-pathfinder/${var.environment}/gateway-id"
+}
+
 # Get current AWS account ID
 data "aws_caller_identity" "current" {}
 
@@ -124,47 +129,6 @@ resource "aws_iam_role_policy" "dynamodb_access" {
   })
 }
 
-# AWS Pricing API access
-resource "aws_iam_role_policy" "pricing_api_access" {
-  name = "airun-pathfinder-crud-pricing-pricing-api-policy"
-  role = aws_iam_role.lambda.id
-
-  policy = jsonencode({
-    Version = "2012-10-17"
-    Statement = [
-      {
-        Effect = "Allow"
-        Action = [
-          "pricing:GetProducts",
-          "pricing:DescribeServices",
-          "pricing:GetAttributeValues"
-        ]
-        Resource = "*"
-      }
-    ]
-  })
-}
-
-# STS AssumeRole access (for Cost Explorer in customer accounts)
-resource "aws_iam_role_policy" "sts_assume_role" {
-  name = "airun-pathfinder-crud-pricing-sts-policy"
-  role = aws_iam_role.lambda.id
-
-  policy = jsonencode({
-    Version = "2012-10-17"
-    Statement = [
-      {
-        Effect = "Allow"
-        Action = "sts:AssumeRole"
-        Resource = "arn:aws:iam::*:role/pathfinder-pricing-access"
-      }
-    ]
-  })
-}
-
-# Cost Explorer access (when assuming role)
-# Note: This is granted via the role in the customer account, not here
-
 # Local variables
 locals {
   table_name = var.table_name != "" ? var.table_name : "pathfinder-${var.environment}-pricing"