feat: add host parameter to allow listening on a specific ip address

[perber]

No description provided.

[Copilot]

Pull Request Overview

This PR adds a host parameter to LeafWiki to allow configuring the IP address the server binds to, enabling deployment scenarios where the server should only listen on specific interfaces (e.g., localhost behind a reverse proxy).

• Added --host CLI flag and LEAFWIKI_HOST environment variable with default value 0.0.0.0
• Updated server startup to bind to the specified host and port combination
• Added documentation explaining the new parameter and its use case with reverse proxies

Reviewed Changes

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

File	Description
readme.md	Added documentation for the new host parameter in CLI flags, environment variables, and usage examples
cmd/leafwiki/main.go	Implemented host parameter handling and updated server binding logic

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