Fixes #43306

Long error messages from LLM providers in the Agent Panel were not
scrollable, making it impossible to read the full error content.

Changes:
- Add max_h_48() and overflow_y_scroll() to description containers
- Add element IDs required for scroll functionality
- Add min_h_0() and overflow_hidden() to parent flex container
- Add component preview example demonstrating scrollable content

Release Notes:

- Fixed long error messages in Agent Panel being unreadable by making
them scrollable
([#43306](https://github.com/zed-industries/zed/issues/43306)).

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Co-authored-by: Danilo Leal <daniloleal09@gmail.com>