feat(tui): completions: dynamically adjust width based on items

* feat: support anthropic provider type in custom provider configs
* docs: fix provider configuration field name and add anthropic example
- Change `provider_type` to `type` in documentation to match actual struct field
- Add comprehensive examples for both OpenAI and Anthropic custom providers
- Include missing `api_key` field in examples for completeness
* feat: resolve headers to allow for custom scripts and such in headers
* feat: allow headers in the anthropic client
* feat: if api_key has "Bearer " in front then using it as an
Authorization header and skip the X-API-Key header in the anthropic
client
* feat: add support for templating in the config resolve.go
something like `Bearer $(echo $ENVVAR)-$(bash ~/.config/crush/script.sh)` would work now; also added some tests since the first iteration of this broke stuff majorly lol
* feat: add a system prompt prefix option to the config
---------
Co-authored-by: Kieran Klukas <me@dunkirk.sh>
Co-authored-by: Kieran Klukas <l41cge3m@duck.com>

perf: init tools and providers in background

* `rm -r ~/.local/share/crush`
* run `crush`
* type something on the filter so no model is shown on the list
* press enter
* a panic happens

Fixes #285

- use this list in the sessions selector

- it should skip unselectable items in the middle

chore(deps): update lipgloss

With this, the completions popup will now reposition itself on
fitlering, resizing, and when the cursor moves. It also ensures that the
completions are correctly positioned relative to the textarea cursor
position.

Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com>

add command allowlist

feat: use new catwalk

fix(tui): app: show error message when window is too small

fix(non-interactive): check bounds when reading message bytes

fix(tui): cursor position in the textarea