Expose only `ripwire-router` and progressively load the other skills

`SKILL` is becoming more popular than `MCP` partly because of its progressive loading, which means there is less prompt added to the context compared with MCP. But a skill's `name` and `description` are still added to the context, even though they are much smaller than MCP tool schemas.

I noticed that `ripwire` has almost 17 skills, and none of them has `disable-model-invocation: true`. So all of these skills' `name` and `description` will be added to the context.

This means that I can start a session, do nothing related to `ripwire`, and still need to pay for the context of all these skills.

I also noticed that the MCP interface of `ripwire` is optional, so I guess that reducing unnecessary context cost is already one of the considerations here.

I noticed that `ripwire` already has a `ripwire-router` skill. So I am wondering whether it would be better to make it the only skill exposed to the model by default, and let it route the agent to the other skills, which could then be loaded progressively.

For example, its content could be something like:

```text
....

- If you need to find a bug - see `./reference/ripwire-find-bug/SKILL.md`
- If you need to xxx - see `./reference/ripwire-fresh-eyes/SKILL.md`
- ....
```

I mean, we can use one entrance skill to index and route the agent to the proper skill, instead of exposing all the skills to the model at the beginning of every session.

I think this may better preserve the progressive-loading advantage of skills.

Just a "brainstorming". I hope this will be helpful. Feel free to point out any mistakes if there are any. And I'd be happy to discuss further.

Start by reviewing the existing ripwire-router skill and the reference/*/SKILL.md files, then trace how all skills are exposed to the model and how the optional MCP interface fits in. Done would mean exposing only ripwire-router by default while allowing it to route agents to the other skills progressively, with the context-cost behavior verified.

Written by the indexing model from the issue text.