fix(chat): give prompt suggestion cards a uniform height (#261)

## What

The **Research topic** entry in the "Suggested messages" carousel has a
short
prompt (`"What are the latest developments in AI?"`) that wraps to
**two** lines
instead of three. Because the suggestion card has no fixed height, that
card
rendered one line shorter than the rest, so its container was smaller
and the
carousel looked uneven.

## Fix

Reserve the full three-line height for the prompt text (matching the
`numberOfLines={3}` cap) so every card is the same size regardless of
prompt
length.

## Before / After

Same two cards in both shots — **Cooking** (3-line prompt) next to
**Research
topic** (2-line prompt).

**Before** — the *Research topic* card ends a line higher than its
neighbours:


![before](https://raw.githubusercontent.com/software-mansion-labs/private-mind/9024c2fb15f4d140af05b70bb2ac468a1c4036ac/before.png)

**After** — all cards share the same height (the shorter prompt just
leaves the
third line empty):


![after](https://raw.githubusercontent.com/software-mansion-labs/private-mind/9024c2fb15f4d140af05b70bb2ac468a1c4036ac/after.png)

Author: kfaracik

components/chat-screen/PromptSuggestions.tsx

@@ -82,5 +82,6 @@ const createStyles = (theme: Theme) =>
       fontFamily: fontFamily.regular,
       color: theme.text.defaultSecondary,
       lineHeight: lineHeights.xs,
+      height: lineHeights.xs * 3,
     },
   });