XMPP channel

[regularfry]

This PR adds XMPP support. I'm offering it with no guarantees other than "it works for me, it might work for you too".

I've got it running against a self-hosted Snikket server which I'm talking to with the Conversations-based Snikket client. File transfers work (so I can show the bot a photo and it's correctly passed off to the multimodal model endpoint as media). I haven't tested anything audio-related.

You'll see that I haven't got to OMEMO encryption yet: that's definitely something I want to do but since I'm running this mainly over my local network and only remotely over a VPN, it's not something I'm overly concerned with personally.

I've not done much outside the channel itself here:

  $ ./core_agent_lines.sh 
nanobot core agent line count
================================

  agent/            1438 lines
  agent/tools/      1460 lines
  bus/                88 lines
  config/            644 lines
  cron/              441 lines
  heartbeat/         178 lines
  session/           218 lines
  utils/             208 lines
  (root)              14 lines

  Core total:     4689 lines

  (excludes: channels/, cli/, providers/, skills/)

Annoyances:

• XMPP can technically, I think, support both media and text in the same message, but the clients I'm using don't. So there's always a bit of "I'm about to show you a picture of... Please can you..." which is a bit unwieldy but does work.
• If you're using a model that likes to talk in Markdown that gets old fast. XMPP formatting isn't as rich and it gets very noisy. It's perfectly legible, it just irritates me. The relevant XMPP formatting standard is XEP-0393; Qwen3.5 (for instance) knows what that formatting is, but getting it to stick to it is very hit or miss.
• Running out of context or getting connection errors just end up with the error popping out as chat messages with just the final exception. I find myself wanting more information than that but I also don't want to swamp my client with stack traces. There's some work to do here.

But, as I said up top: it works for me.

[chengyongru]

Hi @regularfry, thanks for this contribution!

One small suggestion: please target the PR to the nightly instead of . We typically merge new features to nightly first for testing before the next release.

Btw, uv.lock should not be submit.

Otherwise, looking good!

[regularfry]

Ok, will do. I can see how the config is arranged has changed too, I'll realign to that.