Teh

Add PlaceholderAPI support (%teh_enabled%), softdepend, and update README

• Implement PlaceholderAPI expansion: %teh_enabled% returns per-player indicator state
• Register expansion if PlaceholderAPI is present
• Add PlaceholderAPI as softdepend in plugin.yml
• Update README: document PlaceholderAPI usage, features, config, permissions, and commands
• Enable by default