Split view, personal modes, budget warnings, server move script

- Up to three chats side by side (#/s/a+b+c), "Open beside" in the sidebar menu
- File manager tabs of a chat stored per user on the server (/sessions/{id}/tabs)
- Personal modes for every user (Settings → My modes, /account/modes)
- Budget meters (total, provider, images, opencode Go windows) with push warnings
  for admins at the warning share and 100 %, shown in the status overlay
- scripts/move-server.sh: move to another Docker host with bind mounts (Unraid);
  scripts/smoke-test.sh

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/src/runner.rs

@@ -268,7 +268,7 @@ pub async fn run_session(app: Arc<App>, session_id: &str, cancel: CancellationTo
         let cwd = PathBuf::from(&session.cwd);
         let roots = app.user_roots(session.owner_id.as_deref());
         let root = app.root_for(session.owner_id.as_deref(), &cwd);
-        let mut agent = prompts::find_agent(&app, &root, &cwd, &session.agent);
+        let mut agent = prompts::find_agent_for(&app, &root, &cwd, &session.agent, session.owner_id.as_deref());
         let clean_room = session.clean_room(app.config().craft.clean_room);
         // The craft prompt follows the session's clean room / deep switch.
         if agent.name == "craft" && agent.source == "builtin" {
@@ -667,7 +667,7 @@ pub async fn run_subagent(app: Arc<App>, ctx: &ToolCtx, agent: &str, description
 fn create_child(app: &Arc<App>, ctx: &ToolCtx, agent_name: &str, description: &str, prompt: String) -> Result<(Session, Agent)> {
     let parent = app.session(&ctx.session_id)?;
     let root = ctx.root();
-    let parent_agent = prompts::find_agent(app, &root, &ctx.cwd, &parent.agent);
+    let parent_agent = prompts::find_agent_for(app, &root, &ctx.cwd, &parent.agent, parent.owner_id.as_deref());
     let agents = prompts::agents(app, &root, &ctx.cwd);
     let mut agent = agents
         .iter()