feat(panel): introduce new web panel for managing rustmail settings and tickets

[Akinator31]

Add a web administration panel for Rustmail to manage the bot and tickets directly from a web interface. Everything runs in a single binary - both the Discord bot and the web panel are compiled together.

Features

Web Panel (rustmail_panel)

• Web interface built with Rust/WASM (Yew)
• Discord OAuth authentication
• Real-time bot configuration management
• Ticket visualization and management (pagination, search, sorting)
• Multi-language support (FR/EN)

REST API (rustmail/src/api)

• Authentication routes (login, callback, logout)
• Bot management endpoints (start, stop, restart, status)
• Configuration API with dynamic updates
• Ticket retrieval and user avatar APIs
• Session-based authentication middleware

Architecture

• New rustmail_types crate to share types between bot and panel
• Code restructuring: src/ → rustmail/src/
• Permission system for panel users
• Real-time thread status tracking

Migrations

• Added sessions_panel, permissions, and thread_status tables
• Updated scheduled_closure to support new workflows