[Bugs] When using a model from a BYOK provider, project skills fail to load

**Mood:** 😔
**Category:** Bugs

When using a model from a BYOK provider, it seems project skills are detected but fail to load when actualy trying to use thme or invoke them with a slash command.

The reason is silently failing.

This works fine when using models from the GitHub Copilot subscription.

---
| Field | Value |
| --- | --- |
| App version | 1.0.7 |
| OS | macOS 26.5.1 |
| Theme | IC Orange PPL |
| Path | /chat |
| Tenure | Day 3 (Week 1) |

Start by reproducing the failure with a model from a BYOK provider, then compare project-skill loading and slash-command invocation with a GitHub Copilot subscription model. Investigate why the BYOK path fails silently; done means project skills load and can be invoked in both cases, with an actionable error when loading fails.

索引モデルが issue の本文から書いたものです。