feat: basic configuration with environment variables

[nebjak]

No description provided.

[Copilot]

Pull Request Overview

This PR adds basic configuration support via environment variables to TLQ. The main changes replace hardcoded values with configurable options and add comprehensive testing for the configuration system.

• Adds a configuration module that reads settings from environment variables
• Replaces hardcoded constants with configurable values (port, message size limit, log level)
• Updates documentation to explain the new configuration options

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/config/mod.rs	New configuration module with environment variable parsing and comprehensive tests
src/services/mod.rs	Replaces hardcoded MESSAGE_SIZE_LIMIT with configurable max_message_size
src/main.rs	Updates server startup to use configurable port and log level
src/lib.rs	Adds config module to public API
USAGE.md	Documents new configuration options with examples
README.md	Adds configuration section with examples
Dockerfile	Sets default environment variables and updates healthcheck

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