Add configurable voice-note auto-reply with schedule support

[Naude555]

Motivation

• Provide an automatic response when users send WhatsApp voice notes (PTT), with controls to restrict behavior by DM/group/both and to avoid spamming via cooldowns.
• Allow time-aware behavior so operators can enable replies only during working hours or leave them always-on.

Description

• Detect inbound voice notes (audioMessage.ptt) and record them as type: 'voice', logging the event and storing a message record for UI/records.
• Add a new automations.autoReply.voiceNote config (backed by env vars) with enabled, scope (dm|group|both), text, cooldownMs, and schedule (mode: always|hours, start, end, tz) and wire it into the default automations config.
• Implement schedule and cooldown checks in shouldSendVoiceNoteAutoReply and enqueue a queued text reply when the rule passes; expose the effective voice-note auto-reply config in the /health response.
• Document new environment variables in .env.example and README.md so the feature can be configured immediately.

Testing

• Ran node --check server.js to verify syntax and module correctness, which succeeded.

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Codex Task