fix(copilot): honor preset command template overrides

[faqehanoor]

## Summary

Fixes #2761 by updating the Copilot integration to resolve command templates through the existing preset-aware PresetResolver.

Previously, Copilot always used the bundled shared command templates, causing preset-provided command template overrides (such as specify.md) to be ignored. With this change, Copilot now honors preset overrides while preserving the existing fallback behavior when no override is available.

What changed

• Updated the Copilot setup path to resolve command templates using PresetResolver.resolve(..., template_type="command")
• Preserved the existing fallback behavior when no preset override exists
• Added regression tests for:
  • Default fallback behavior
  • Preset override behavior

Testing

ruff check src/specify_cli/integrations/copilot/init.py tests/integrations/test_integration_copilot.py

pytest -q tests/integrations/test_integration_copilot.py