docs: complete plugin and security documentation

[variablenix]

Summary

• document all six new plugins, commands, aliases, limits, config, and environment variables
• document the one-line response guarantee and port catalog scope
• document paste URL-fetching security boundaries and add paste variables to .env.example
• remove the unused port.max_length setting from configuration examples

Validation

• git diff --check
• config YAML parse
• go test ./...