Custom provider with multisession support

I’m not sure if there’ll be interest in implementing it in the plugin core, but I hacked a custom provider that adds two features:
- **Tab-scoped sessions**: Each Neovim tab gets its own independent Claude Code session. I can run multiple sessions within the same branch, or have agents working autonomously on different worktrees while I focus on something else.
- **Layout switching**: Sometimes I have long discussions with an agent without referencing code much. In those cases, I prefer a centered floating window over the side panel. The provider supports two layouts—`side` and `float`—and I can toggle between them with a keybind.

Multisession required a [few patches](https://github.com/alex35mil/dotfiles/blob/master/home/.config/nvim/lua/editor/features/claudecode-provider.lua#L268-L445), but it works.

I put all details in the blog post: https://alex.draft42.io/blog/multisession-agentic-workflow-with-claude-code-in-neovim-lsdoiuzd0

Provider source: https://github.com/alex35mil/dotfiles/blob/master/home/.config/nvim/lua/editor/features/claudecode-provider.lua
Provider + plugin config: https://github.com/alex35mil/dotfiles/blob/master/home/.config/nvim/lua/plugins/ai/claudecode.lua

Inizia leggendo la sorgente del provider collegata e le patch di multisession intorno alle righe 268-445, quindi confrontale con l’architettura attuale dei provider del plugin. Usa il post del blog collegato e la configurazione come contesto per le sessioni richieste associate alle tab e per il passaggio tra i layout side/float; il lavoro sarebbe completato quando si sarà concordato e integrato un design core appropriato.

Scritto dal modello di indicizzazione a partire dal testo della issue.