Align README and in-app help with current commands and configuration

Problem

Several user-facing references have drifted from the implementation:

• The README command table calls ReverseTrackOrder ReverseOrder.
• Command::desc hardcodes a five-second default for seek commands even when seek_duration_secs is configured differently.
• The configuration note says a positive app_refresh_duration_in_ms increases API usage, but API playback polling is controlled by playback_refresh_duration_in_ms.
• The README CLI overview omits the generate, features, and lyrics subcommands.

Expected behavior

The README, configuration guide, and in-app help should describe the same command names and effective configuration.

Acceptance criteria

• Command names match the Rust variants accepted by configuration.
• Seek help reflects the configured default or avoids claiming a hardcoded value.
• The refresh-rate note names the option that performs API polling.
• The CLI overview includes all supported top-level subcommands.
• A lightweight consistency check is considered for command tables to reduce future drift.