fix: delete instance cleanup on baileys failure

[antonio-abrantes]

📋 Description

🐛 Problem

When calling DELETE /instance/delete/{instanceName} on a corrupted
instance (disconnected/bugged Baileys session), the API returns:

{
  "status": 400,
  "error": "Bad Request",
  "response": { "message": ["[object Object]"] }
}

After this error, the instance name remains permanently blocked in
waInstances memory. Even after manually cleaning the database, Redis,
and session files, calling POST /instance/create with the same name
returns:

{
  "status": 403,
  "message": ["This name \"agent-xxx\" is already in use."]
}

The only workaround was restarting the container — not viable in production environments.

---

🔍 Root Cause

Two bugs working together:

1. Aborted cleanup

• deleteInstance() stopped execution if logout() failed

2. Bad error serialization

• Errors returned as [object Object]

---

✅ Fix

• Split try/catch into isolated steps

• Ensure cleanup always runs

• Always remove instance from waInstances

• Fix error serialization using:

  error?.message ?? String(error)
  

---

🔗 Related Issue

Closes # (leave empty if not applicable)

---

🧪 Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature
• 💥 Breaking change
• 📚 Documentation update
• 🔧 Refactoring
• ⚡ Performance improvement
• 🧹 Code cleanup
• 🔒 Security fix

---

🧪 Testing

• Manual testing completed
• Functionality verified in development environment
• No breaking changes introduced
• Tested with different connection types

---

📸 Screenshots (if applicable)

N/A

---

✅ Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• My changes generate no new warnings
• I have manually tested my changes thoroughly
• I have verified the changes work with different scenarios

---

📝 Additional Notes

Tested in production environment with Docker Swarm + PostgreSQL + Redis.
Fix only affects failure path — no impact on healthy instances.

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