v0.10.0 — LLM auto-detection + config show/test

Answer to "how does the user configure the LLM?": just set any provider's API key. autokernel now auto-detects which providers you have credentials for and picks a sensible model.

What's new

Auto-detection across 8 provider families

Set any of these in your shell or `.env`:

```bash
export ANTHROPIC_API_KEY=sk-ant-...
export OPENAI_API_KEY=sk-...
export GOOGLE_API_KEY=... # or GEMINI_API_KEY
export MISTRAL_API_KEY=...
export GROQ_API_KEY=...
export XAI_API_KEY=...
export DEEPSEEK_API_KEY=...
export OPENROUTER_API_KEY=...
```

`autokernel propose` picks the first available provider; `--llm-mode` chooses a preset:

```
auto -> sonnet-4-6 / gpt-5 / gemini-2.0-flash / ...
cheap -> haiku-4-5 / gpt-5-mini / gemini-2.0-flash-lite / ...
quality -> opus-4-7 / gpt-5 / gemini-2.5-pro / ...
```

`autokernel config` sub-app

```bash
autokernel config show # render resolved config + provider table
autokernel config show --mode quality # what would --llm-mode=quality pick?
autokernel config test # ping the model with a one-token prompt (~$0.001)
```

Better errors

When no provider is configured, the error names exactly which env vars to set. When you ask for `openai:gpt-5` but only have `ANTHROPIC_API_KEY`, the error names `OPENAI_API_KEY` as the fix.

Tests

514 total, ~4s. 33 new tests cover provider detection, mode resolution, error paths, and the config sub-app.