Add ban system, version notifications, and admin improvements

[plop91]

Major features:

• User ban system with timed/permanent bans (ban, unban, banlist commands)
• Version update notifications to configured announcement channels
• Voice channel auto-disconnect after 10 minutes of inactivity
• Implement hash and version admin commands

Improvements:

• Add check decorators (is_admin, in_command_channel, not_banned)
• Apply not_banned decorator across all user-facing commands
• Consolidate Dockerfile and Dockerfile-dev into single configurable Dockerfile
• Add CONFIG_FILE env var for flexible config selection

New files:

• CLAUDE.md: Project documentation for development
• DISCLAIMER.md: Data usage policy
• .env.example: Environment variable template

Bug fixes:

• Fix variable scoping in is_banned() causing UnboundLocalError