feat: add autoSendInitialMessage config option for pre-populating chat

[SyncWithRaj]

What was the problem?

Previously, if a developer wanted to pre-populate and send an initial message when the chat widget loads, they had to mutate the DOM directly via JavaScript (e.g., setting the input field's value and clicking the send button programmatically). This doesn't work well with Solid.js because the internal reactive state stays empty, leaving the Send button disabled.

Closes #343

What was built?

A new config option called autoSendInitialMessage. This allows developers to pass any custom message string via the embed config. The widget will automatically type it into the input field and submit it as soon as the chat loads using Solid.js's reactive state system.

It uses a hasAutoSentInitialMessage flag to ensure the automatic message only fires exactly once upon initialization.

How end-users use it:

Chatbot.init({
    chatflowid: 'your-chatflow-id',
    apiHost: '[https://your-api-host.com](https://your-api-host.com)',
    theme: {
        chatWindow: {
            autoSendInitialMessage: 'Hello, I need help with my order!',
        },
    },
})

Technical Changes:

• src/features/bubble/types.ts: Added autoSendInitialMessage?: string to ChatWindowTheme interface.

• src/components/Bot.tsx: Added the prop to BotProps. Added logic inside the config-loading createEffect to set the reactive input value and trigger handleSubmit() once the config is fully fetched.

• src/features/bubble/components/Bubble.tsx & src/features/full/components/Full.tsx: Passed the new config property down to the Bot component.

• src/window.ts & src/constants.ts: Cleaned up the prop flow so it routes cleanly through the theme object.

Testing:

• Tested in popup bubble mode.
• Tested in full-page embed mode.
• Verified that if the property is omitted or empty, the chat behaves normally.
• Confirmed the build (yarn build) compiles successfully without TS errors.

[gemini-code-assist]

Code Review

This pull request introduces the autoSendInitialMessage feature, enabling the chatbot to automatically send a message upon initialization. The implementation includes updates to the Bot component, theme types, and the bubble/full-page features. Review feedback points out that the auto-send logic incorrectly triggers on page refreshes even with existing history and should be moved inside the configuration loading block to prevent race conditions. Additionally, the state flag tracking the auto-send status should be reset when the chatflowid changes to support component reuse in single-page applications.