Add /vc command suite with low-overhead voice activity tracking, blacklist controls, and hourly top-10 reporting

[Copilot]

This change introduces a voice-activity feature set that mirrors the existing /setup command UX/style and storage conventions, while adding voice-specific tracking, blacklist management, and periodic leaderboard output. It uses join/leave/session transitions (not polling) to keep runtime overhead low and aligns logs with the configured setup logs channel.

• /vc command group aligned to /setup behavior

  • Added a new /vc command suite with setup-style subcommand structure, messaging theme, and permission/guard patterns.
  • Kept interaction and embed formatting consistent with existing setup/log presentation, adapted for voice activity semantics.

• Event-driven VC tracking model (low server pressure)

  • Implemented tracking via on_voice_state_update using session start/end timestamps.
  • Handles:
    • join → start session
    • leave → close session, compute elapsed, accumulate total
    • channel switch → close previous session + start new one
  • Ignores bot users and includes defensive handling for missing/partial session state after restarts.

• Storage and compatibility

  • Added voice-activity persistence using the repository’s existing DB/storage conventions used by setup/text tracking.
  • Persists cumulative per-user VC time and required session/log data without changing current text-tracking behavior.

• VC blacklist management

  • Added /vc blacklist controls to add/remove/list/check excluded voice channels.
  • Added channel selection UX using voice-channel suggestion patterns (autocomplete/picker behavior consistent with existing command patterns).
  • Blacklisted voice channels are excluded from tracked time.

• Logging + hourly leaderboard

  • Integrated with the configured logs channel from setup configuration.
  • Added join/leave logs for counted VC channels including:
    • per-session duration on leave
    • updated cumulative total after aggregation
  • Added lightweight hourly top-10 VC activity message based on cumulative tracked time, following existing theme style.

# Voice state transition pattern used for low-overhead tracking
if before.channel != after.channel:
    if before.channel and is_counted(before.channel):
        elapsed = end_session(member.id)
        total = add_to_cumulative(member.id, elapsed)
        await log_leave(member, before.channel, elapsed, total)

    if after.channel and is_counted(after.channel):
        start_session(member.id)
        await log_join(member, after.channel)