Both `+ New` buttons (AI panel and dashboard) now dispatch
`SessionCommand::Spawn`, which always forks a new worktree off the
project's `default_branch`. Removes the divergent
`session_spawn_at_root` / `session_spawn_new_worktree` helpers — the
AI panel previously forked off the active worktree's HEAD, so the
second click in a row landed on the wrong branch.

The AI panel session strip and a new dashboard `Agents` section both
read from every Context's `ai_sessions`, so running agents stay
visible regardless of which Context is active. Click an agent in
either surface to dispatch `SessionCommand::Switch`, which routes
through the existing per-Context focus + Context-switch logic.

Ratchet: `session_command::CkEditorApp` cyclomatic 25 → 24, RFC 26 → 24.

@@ -82,0 +85,4 @@
+    for ctx in p.contexts.values() {
+        for (key, session) in &ctx.ai_sessions {
+            tabs.push(ai_panel::SessionTab {
+                key: key.clone(),

@@ -368,0 +405,4 @@
+    out: &mut DashboardAction,
+) {
+    show_section_header(ui, SECTION_AGENTS, theme);
+    let mut entries: Vec<(String, String, Color32)> = Vec::new();

@@ -111,0 +95,4 @@
+    // worktree). Used only by `SpawnForBranch` when the caller is already
+    // on the target branch and no worktree exists for it. The AI panel
+    // `+ New` button does NOT come here — it always creates a worktree.
+    fn session_spawn_in_project_root(&mut self, ctx: &egui::Context) {