feat: Enhanced GitHub OAuth with User Profile Management

- Added secure token exchange Lambda
- Added GitHub user info Lambda
- Added user profile management with DynamoDB
- Added logging middleware
- Updated CDK stack with new resources
- Removed client secret from frontend
- Fixed Go module structure

Closes fynnfluegge#74
Addresses security concerns from PR fynnfluegge#145

cdk/functions/user-profile/go.mod

@@ -0,0 +1,11 @@
+module github.com/fynnfluegge/rocketnotes/cdk/functions/user-profile
+
+go 1.21
+
+require (
+    github.com/aws/aws-lambda-go v1.46.0
+    github.com/aws/aws-sdk-go-v2 v1.25.3
+    github.com/aws/aws-sdk-go-v2/config v1.27.7
+    github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue v1.13.9
+    github.com/aws/aws-sdk-go-v2/service/dynamodb v1.30.4
+)