Fish shell not supported

`vibe init` writes bash/zsh hook syntax. Fish uses different function syntax and `config.fish` instead of `.zshrc`.

## Workaround

Add the hook manually to `~/.config/fish/config.fish`:

```fish
function claude
  vibe __wrap claude $argv
end
```

## Fix

Detect fish shell in `init.ts` and write fish-compatible syntax.