Complete foundational data layer with repository implementation

- Add GORM dependencies for SQLite and PostgreSQL
- Create domain models (User, Session, File) with common errors
- Implement repository interfaces and database layer with migrations
- Update WebApp to bootstrap with database and repositories
- Add comprehensive unit tests for repository methods
- Update config structure to support multiple database drivers
- Extend AGENTS.md with debugging principles and dependency rules

internal/server/server_test.go

@@ -11,7 +11,7 @@ import (
 )
 
 func TestVersionRoute(t *testing.T) {
-	webApp := app.NewWebApp(&config.Config{})
+	webApp := app.NewWebApp(&config.Config{}, nil, nil, nil, nil)
 	router := NewRouter(webApp)
 
 	req := httptest.NewRequest(http.MethodGet, "/api/v1/version", nil)