fix(compare): find the chat outside the widget's own index

[Haroenv]

Summary

compare() resolved the chat only from the render state of the widget's own index, while the selection store is shared across the whole InstantSearch instance. A compareBar in a nested index with the chat at the root (or the reverse) therefore returned false with no feedback.

The lookup now lives in a shared helper, getChatRenderState(instantSearchInstance, indexId) in src/lib/chat/, with a deterministic order: the chat in the widget's own index, then the main index, then the first other index that rendered a chat. compare() emits a dev-mode warning when no chat is mounted.

Result

• compare() opens the chat and sends the comparison regardless of which index the chat or the compare widget is mounted in.
• compare() warns in development when no chat is found.
• Tests cover a nested compare widget with a root chat, the lookup order, and the warning.
• connectChatTrigger is unchanged.

🤖 Generated with Claude Code

[codacy-production]

Up to standards ✅

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🟢 Metrics 15 complexity

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[Haroenv]

Follow-up: connectChatTrigger has the same own-index-only lookup (its local getChatRenderState reads renderState[ownIndexId].chat), so a chatTrigger in a nested index won't find a chat mounted at the root. Its open/isChatBusy render state and toggleOpen all go through that lookup, so switching it to the shared lib/chat/getChatRenderState helper changes more than the hand-off. Left out of this PR on purpose.

— via Claude