feat: multi session chat

[chloebyun-wd]

Adding in multi session chat experience:

Chatbot.initFull({
            chatflowid: 'agent1',    // or 'support', 'salesbot', etc.
            apiHost: window.location.origin,
            multiSession: { enabled: true }  // this is the new config to enable the new experience
        })

What's new (multi-session only)

• Session panel + title header — sidebar in full-page mode, drawer in bubble/popup, transparent ChatGPT-style header with Star/Rename/Delete menu;
• Sessions store — new/switch/upsert/rename/delete + toggleStarred, per-chatId debounced persistence, cross-tab storage-event sync with active-stream protection, quotaPanic signal for unrecoverable storage failures, cap-eviction with capWarning toast.
• Storage layer — v1→v2 in-place migration that preserves legacy lead, orphan reconciliation, defensive safeParse with logging.
• Bot.tsx hardening — streamingChatId pin so tokens never bleed across mid-stream session switches, best-effort abortMessageQuery on switch, empty-placeholder cleanup, clearChatOnReload guarded against the v2 index, SSE body uses pinned chatId.
• New TextInput / SendButton variant — two-row layout with rounded send pill and UpArrowIcon, while non-multi keeps main's exact single-row layout.
• Latest-user-message scroll anchor — pins the user's message near the top per turn (matches ChatGPT). Non-multi keeps main's plain scroll-to-bottom.

[gemini-code-assist]

Code Review

This pull request introduces a multi-session feature for the chatbot, allowing users to manage multiple conversations. It includes a new session store, storage migration logic, and UI components like the SessionPanel and SessionListItem. I have reviewed the changes and identified two areas for improvement: the send button's background color fallback logic in TextInput.tsx and the missing background color prop for the LoadingBubble in Bot.tsx.

[gemini-code-assist]

The fallback logic for the send button's background color is a bit confusing. It falls back to props.sendButtonColor, which is intended for the icon color, not the background. This could lead to unexpected styling if sendButtonBackgroundColor is not provided. For clarity and correctness, it would be better to remove the fallback to sendButtonColor and just use the default color.

Suggested change

	style={{ background: props.sendButtonBackgroundColor ?? props.sendButtonColor ?? '#3B81F6' }}
	style={{ background: props.sendButtonBackgroundColor ?? '#3B81F6' }}

[gemini-code-assist]

The LoadingBubble component now supports a backgroundColor prop, but it's not being passed here. This will result in a transparent background for the loading bubble, which might be inconsistent with the BotBubble's background, especially in multi-session mode. To ensure visual consistency, you should pass the botMessage background color to the LoadingBubble.

Suggested change

	{message.type === 'userMessage' && loading() && index() === messages().length - 1 && <LoadingBubble />}
	{message.type === 'apiMessage' && message.message === '' && loading() && index() === messages().length - 1 && (
	<LoadingBubble />
	)}
	{message.type === 'userMessage' && loading() && index() === messages().length - 1 && <LoadingBubble backgroundColor={props.botMessage?.backgroundColor} />}
	{message.type === 'apiMessage' && message.message === '' && loading() && index() === messages().length - 1 && (
	<LoadingBubble backgroundColor={props.botMessage?.backgroundColor} />
	)}