feat: add integration tests for various frameworks and update configurations

[Polliog]

This pull request introduces the new @logtide/express package and makes several improvements to the repository structure, documentation, and CI workflow. The most significant changes are the addition of Express middleware support, updates to the monorepo documentation, and enhancements to the CI pipeline to better separate and clarify testing stages.

Major changes in this pull request:

New Package: Express Middleware

• Added the new @logtide/express package, providing Express middleware for automatic request tracing, error capture, breadcrumbs, and W3C Trace Context propagation. Includes TypeScript types, documentation, and full configuration support. (packages/express/README.md, packages/express/package.json, packages/express/src/index.ts) [1] [2] [3]

Monorepo Structure and Documentation

• Updated the root README.md to include @logtide/express and @logtide/fastify, clarify the legacy status of @logtide/sdk-node, and update the architecture diagram accordingly. [1] [2]
• Added a detailed CHANGELOG.md describing all notable changes, including the new monorepo structure, package features, and CI/CD improvements.
• Added CONTRIBUTING.md and CODE_OF_CONDUCT.md to guide contributors and set community standards. [1] [2]
• Added an explicit LICENSE file (MIT License).

Continuous Integration Improvements

• Refactored the GitHub Actions workflow to split tests into unit tests, smoke tests (for various frameworks), and E2E tests (for Next.js, SvelteKit, and Nuxt), providing clearer test stages and improved reliability. [1] [2]

Scripts and Package Management

• Updated package.json scripts to add test:smoke, test:e2e, and test:all for more granular test control and to scope build/test commands to @logtide/* packages.

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These changes collectively improve framework support, developer experience, and project maintainability.