Wire up voice channel XP tracking

[gvieira18]

Context

Voice XP tracking is completely non-functional. The infrastructure exists
but nothing is wired together — users in voice channels always get 0 XP.

What exists today

• DynamicVoiceEvent captures Discord VOICE_STATE_UPDATE and calls
  PersistVoiceStateAction, which stores records with
  obtained_experience = 0 always.
• NewVoiceMessage (the action that would calculate and award XP) is
  never called anywhere — dead code.
• IncrementExperience::incrementByVoiceMessage() works correctly and
  is tested, but never invoked for voice.
• Mute/deaf state is never captured — Discord sends self_mute /
  self_deaf but the code only tracks join/leave.
• Schema mismatch — voice_messages.state stores 'joined'/'left'
  strings, but VoiceStatesEnum expects {disabled, muted, unmuted}.

How the old bot handled it

The previous Node.js bot (he4rt-bot-next) used a ticker/polling
approach that worked well:

// Every VOICE_COUNTER_XP_IN_MINUTES, scan all members in voice channels
const isUnmuted = !member.voice.selfMute && !member.voice.serverMute
const isAble = !member.voice.selfDeaf && !member.voice.serverDeaf

state: isAble && !isUnmuted ? 'muted'
     : isAble && isUnmuted  ? 'unmuted'
     : 'disabled'

This maps directly to the existing VoiceStatesEnum multipliers:

• unmuted → 5 × level
• muted → 3 × level
• disabled → 0 × level

What needs to happen

1. Decide approach: replicate the ticker/polling model (scheduled
   command that scans voice channels every N minutes) or fix the
   event-driven flow. Ticker is simpler and proven.
2. Capture mute/deaf state from Discord's voice state data and map
   to VoiceStatesEnum.
3. Call IncrementExperience::incrementByVoiceMessage() to actually
   award XP.
4. Fix or replace NewVoiceMessage — currently depends on the old
   FindExternalIdentity pattern and request()->tenant_id (breaks in
   queue/scheduler context). Should use ResolveUserContext like
   NewMessage does.
5. Reconcile schema — voice_messages.state should store
   VoiceStatesEnum values (disabled/muted/unmuted), not
   joined/left.
6. Exclude AFK channel — old bot skipped the AFK voice channel, same
   logic should apply.
7. Add tests for the full voice XP flow.