feat(epic2): Implement core authentication and authorization services

- Implement Audit Service (2.5)
  - gRPC server with Record and Query operations
  - Database persistence with audit schema
  - Service registry integration
  - Entry point: cmd/audit-service

- Implement Identity Service (2.2)
  - User CRUD operations
  - Password hashing with argon2id
  - Email verification and password reset flows
  - Entry point: cmd/identity-service
  - Fix package naming conflicts in user_service.go

- Implement Auth Service (2.1)
  - JWT token generation and validation
  - Login, RefreshToken, ValidateToken, Logout RPCs
  - Integration with Identity Service
  - Entry point: cmd/auth-service
  - Note: RefreshToken entity needs Ent generation

- Implement Authz Service (2.3, 2.4)
  - Permission checking and authorization
  - User roles and permissions retrieval
  - RBAC-based authorization
  - Entry point: cmd/authz-service

- Implement gRPC clients for all services
  - Auth, Identity, Authz, and Audit clients
  - Service discovery integration
  - Full gRPC communication

- Add service configurations to config/default.yaml
- Create SUMMARY.md with implementation details and testing instructions
- Fix compilation errors in Identity Service (password package conflicts)
- All services build successfully and tests pass

shell.nix

@@ -0,0 +1,81 @@
+{ pkgs ? import <nixpkgs> {
+    config = {
+      allowUnfree = true; # Allow unfree packages like Consul (BSL 1.1)
+    };
+  }
+}:
+
+let
+  go = pkgs.go_1_24;
+in
+
+pkgs.mkShell {
+  buildInputs = with pkgs; [
+    # Go compiler
+    go
+    
+    # Protocol Buffers compiler
+    protobuf
+    
+    # Go tools (available in nixpkgs)
+    go-tools  # Includes goimports, gopls, etc.
+    golangci-lint
+    
+    # gRPC tools for testing
+    grpcurl
+    
+    # Build tools
+    gcc
+    glibc
+    
+    # Version control
+    git
+    
+    # Database tools (optional, for local development)
+    postgresql
+    
+    # Service discovery (optional, for local development)
+    consul
+    
+    # Docker tools (optional, for docker-compose)
+    docker
+    docker-compose
+  ];
+  
+  # Set up environment variables and install Go tools
+  shellHook = ''
+    # Set Go environment
+    export GOPATH="$HOME/go"
+    export GOBIN="$GOPATH/bin"
+    export PATH="$PATH:$GOBIN"
+    export PATH="$PATH:${go}/bin"
+    
+    # Install Go tools if not already installed
+    if ! command -v protoc-gen-go > /dev/null 2>&1; then
+      echo "Installing protoc-gen-go..."
+      ${go}/bin/go install google.golang.org/protobuf/cmd/protoc-gen-go@latest
+    fi
+    
+    if ! command -v protoc-gen-go-grpc > /dev/null 2>&1; then
+      echo "Installing protoc-gen-go-grpc..."
+      ${go}/bin/go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest
+    fi
+    
+    # Verify tools are available
+    echo ""
+    echo "=== Development Environment Ready ==="
+    echo "Go version: $(${go}/bin/go version)"
+    echo "protoc version: $(protoc --version 2>/dev/null || echo 'not found')"
+    echo "golangci-lint version: $(golangci-lint --version 2>/dev/null || echo 'not found')"
+    echo "grpcurl version: $(grpcurl --version 2>/dev/null || echo 'not found')"
+    echo ""
+    echo "Go tools:"
+    echo "  protoc-gen-go: $(command -v protoc-gen-go > /dev/null 2>&1 && echo '✓ installed' || echo '✗ not found')"
+    echo "  protoc-gen-go-grpc: $(command -v protoc-gen-go-grpc > /dev/null 2>&1 && echo '✓ installed' || echo '✗ not found')"
+    echo "  goimports: $(command -v goimports > /dev/null 2>&1 && echo '✓ installed' || echo '✗ not found')"
+    echo "======================================"
+    echo ""
+  '';
+}
+
+