feat: add Firefox AI sidebar (?q=) support to dashboard

[ArvidSU]

This PR builds on #1677 to enable custom prompts sent from Firefox browser.ml.chat to EXO dashboard using URL parameters in sidebar for summary and other browser interactions. See "Summarize page" example below.

Summary

• Parse ?q=<encoded prompt> URL parameter on page load and auto-submit it as a chat message
• Clean up the URL with history.replaceState to prevent re-submission on refresh
• Defer auto-send until both cluster state and model list are loaded so model auto-selection works correctly

Context

Firefox's built-in AI sidebar (about:config: browser.ml.chat.enabled) integrates with chat providers by appending the user's prompt as ?q=<URL-encoded prompt>. Previously the exo dashboard ignored this parameter. Users can now configure http://localhost:52415 as a Firefox AI chatbot provider.

See: https://support.mozilla.org/en-US/kb/ai-chatbot

Technical notes

• Frontend-only change in dashboard/src/routes/+page.svelte
• Uses a Svelte $effect that reacts to pendingFirefoxQuery, data (cluster state), and models.length — fires exactly once when all three are ready
• If no model is selected, handleAutoSend auto-picks the best available model; if no model fits memory, a toast is shown
• If a model is selected but not running, the message is queued until the model loads

Testing

http://localhost:52415/?q=Hello+world
http://localhost:52415/?q=Summarize+this+page%3A+%5Bpage+title%5D+%5Bpage+url%5D

[rltakashige]

Hey - this is really cool; it looks good to me, but I think it would be better if we put this at a /firefox endpoint so that we don't reserve the top-level ?q= for only Firefox.

[ArvidSU]

@rltakashige Hmmm, I see the confusion with my variable naming and comments. However, there is not really anything functional that makes this Firefox specific, the ?q= param is more a de facto convention used by google and chatgpt etc. Since the url is configurable in firefox I can move it to a firefox specific path but my suggestion is to generalize the naming of variables and comments to align with convention. What do you think?

[rltakashige]

Tried to think of an example where we might want to use the ?q= with anything else, but we agreed this seems like a sensible default. We can always move it if it ever becomes necessary.

Thanks for this contribution - I might add this to our integrations in #1810 .