Extract defaults to constants

[jameshiew]

Summary

• define constants for defaults like host, port, log settings, and index HTML
• use constants in config, logging, handler and model defaults

Testing

• cargo build
• cargo test
• ❌ cargo +nightly fmt (fails: unsuccessful tunnel)
• ❌ rustup component add rustfmt (fails: unsuccessful tunnel)

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https://chatgpt.com/codex/tasks/task_e_68401c443d00832687b33259bbeebe0c

[Copilot]

Pull Request Overview

This pull request extracts default configuration values into constants to improve maintainability and consistency.

• Defined constants for default logging settings in src/logging.rs
• Defined constants for server defaults in src/config.rs

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/logging.rs	Added DEFAULT_LOG_ANSI and DEFAULT_LOG_LEVEL constants and updated logger initialization.
src/config.rs	Added DEFAULT_HOST and DEFAULT_PORT constants and updated get_server_addr to use these values.