comfy skills install --skill comfy-build silently skips on every released CLI

`comfy skills install --skill comfy-build` cannot install the skill on any published release. It reports `skipped`, exit 0.

## What happens

```
$ comfy skills install --skill comfy-build --dry-run
│ comfy-build │ claude-code │ skipped │ ~/.claude/skills/comfy-build/SKILL.md │
│ comfy-build │ cursor │ skipped │ ~/.cursor/rules/comfy-build.mdc │
│ comfy-build │ agents-md │ skipped │ ~/AGENTS.md │
│ comfy-build skipped: could not fetch
│ https://raw.githubusercontent.com/Comfy-Org/comfy-skills/main/comfy-cli/comfy-build/SKILL.md: HTTP Error 404: Not Found
```

## Why

`v1.18.0` fetches the skill at install time from a path that no longer exists:

```python
# comfy_cli/skills/__init__.py (v1.18.0)
REMOTE_SKILLS = (RemoteSkill(name="comfy-build", repo="Comfy-Org/comfy-skills",
ref="main", path="comfy-cli/comfy-build/SKILL.md"),)
```

The skill moved into this repository in `4a86b7c` (BE-9486), which deleted it from `Comfy-Org/comfy-skills`. `main` is fine because the bundling commit dropped the remote fetch, but `v1.18.0` is the version on PyPI and it still points at the dead path. Verified: that URL returns 404, and `git ls-tree v1.18.0 comfy_cli/skills/` has no `comfy-build`.

## Impact

Anyone on `pip install comfy-cli` today asks for the skill and is told `skipped` with a 404 they cannot act on. `comfy skills list` compounds it by showing a description that reads as though the skill is available: `Fetched from Comfy-Org/comfy-skills (main) by 'comfy skills install'.`

## Suggested fix

A release carrying `4a86b7c` resolves it. If a release is not imminent, consider restoring `comfy-cli/comfy-build/SKILL.md` in `Comfy-Org/comfy-skills` as a pointer or a copy so the pinned `ref="main"` fetch stops 404ing for users already on 1.18.0.

Found while driving the skill end to end against a real builder.