feat(handler) Support serving static files

[imdhemy]

This PR adds a small built-in middleware to serve static files. The files are served by default from the public directory, and the default index file is index.html, but these options are still configurable.

Available options:

• staticFiles: The parent key of the configuration:
  • root: Configures the root directory of the static files. Defaults to public
  • index: Configures the index file name. Defaults to index.html

Closes #74

[Copilot]

Pull Request Overview

This PR introduces built-in middleware for serving static files from a configurable directory. The implementation delegates to @koa/send and allows customization of the root directory (defaults to public) and index file (defaults to index.html).

Key changes:

• New serveStaticFiles middleware with 404 error handling that falls through to the next middleware
• Configuration interface StaticFilesOptions added to KoalaConfig for customizing static file serving behavior
• Added @koa/send dependency for file serving functionality

Reviewed Changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Http/Files/StaticFilesMiddleware.ts	Core middleware implementation that wraps @koa/send with error handling
src/Http/Files/types.ts	TypeScript interface defining static files configuration options
src/Http/Files/index.ts	Barrel export for the Files module
src/Http/Error/types.ts	HttpError class extending Koa's HttpError for type safety
src/Http/Error/index.ts	Barrel export for the Error module
src/Config/types.ts	Updated KoalaConfig interface to include optional staticFiles configuration
src/Application/ApplicationFactory.ts	Integrated static files middleware into the application factory
src/Application/ApplicationFactory.test.ts	Integration test verifying static file serving from custom directory
src/Http/Files/StaticFilesMiddleware.test.ts	Unit tests for middleware functionality including 404 handling
tests/fixtures/sample.txt	Test fixture file for integration testing
package.json	Added @koa/send dependency
package-lock.json	Dependency updates including @koa/send and various package version bumps
eslint.config.js	Removed @typescript-eslint/consistent-type-exports rule

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