feat: instant draft-first worktree creation and multi-run launcher redesign (#741)

## Summary

- **Instant worktree creation from chat draft**: selecting "+ New worktree" in the draft branch selector immediately creates a session draft and bootstraps the worktree in the background — no modal interruption
- **Redesigned multi-run launcher**: compact 2-column grid layout in a right-sized dialog with scroll shadow, sticky footer, tooltips replacing verbose descriptions, and project icons in the selector
- **Branch selector aligned across surfaces**: multi-run and agent manager branch pickers now use the shared git store and match NewWorktreeDialog behavior (same default resolution cascade, no synthetic HEAD option, all branches shown)
- **Opaque model multi-select dropdown**: fixes text bleed-through on translucent backgrounds by compositing `--surface-elevated` over `--surface-background`
- **"+ New" inline button in sidebar worktree headers** for faster worktree creation

## Why

Worktree creation was behind modal flow that interrupted the user's train of thought. The draft-first approach lets users start typing immediately while the worktree bootstraps. The multi-run launcher had an oversized form layout with redundant explanations, and its branch picker behaved differently from the main worktree dialog - causing confusion about which branches were available and what the default was.

packages/ui/src/components/session/SessionDialogs.tsx

@@ -66,6 +66,9 @@ export const SessionDialogs: React.FC = () => {
         archiveSessions,
         loadSessions,
         getWorktreeMetadata,
+        newSessionDraft,
+        setNewSessionDraftTarget,
+        setDraftBootstrapPendingDirectory,
     } = useSessionStore();
     const showDeletionDialog = useUIStore((state) => state.showDeletionDialog);
     const setShowDeletionDialog = useUIStore((state) => state.setShowDeletionDialog);
@@ -381,12 +384,34 @@ export const SessionDialogs: React.FC = () => {
         deleteLocalBranch: boolean
     ): Promise<boolean> => {
         const shouldRemoveRemote = deleteDialogShouldRemoveRemote && canRemoveRemoteBranches;
+        const projectRef = getProjectRefForWorktree(worktree);
+        const normalizedWorktreePath = normalizeProjectDirectory(worktree.path);
+        const normalizedProjectPath = normalizeProjectDirectory(projectRef.path);
         try {
             await removeProjectWorktree(
-                getProjectRefForWorktree(worktree),
+                projectRef,
                 worktree,
                 { deleteRemoteBranch: shouldRemoveRemote, deleteLocalBranch }
             );
+
+            const draftDirectory = normalizeProjectDirectory(newSessionDraft?.directoryOverride);
+            if (
+                newSessionDraft?.open
+                && normalizedWorktreePath
+                && draftDirectory === normalizedWorktreePath
+                && normalizedProjectPath
+            ) {
+                setDraftBootstrapPendingDirectory(null);
+                setNewSessionDraftTarget({
+                    projectId: projectRef.id,
+                    directoryOverride: normalizedProjectPath,
+                }, { force: true });
+            }
+
+            if (normalizeProjectDirectory(currentDirectory) === normalizedWorktreePath && normalizedProjectPath) {
+                useDirectoryStore.getState().setDirectory(normalizedProjectPath, { showOverlay: false });
+            }
+
             return true;
         } catch (error) {
             toast.error('Failed to remove worktree', {
@@ -394,7 +419,7 @@ export const SessionDialogs: React.FC = () => {
             });
             return false;
         }
-    }, [canRemoveRemoteBranches, deleteDialogShouldRemoveRemote, getProjectRefForWorktree]);
+    }, [canRemoveRemoteBranches, currentDirectory, deleteDialogShouldRemoveRemote, getProjectRefForWorktree, newSessionDraft?.directoryOverride, newSessionDraft?.open, setDraftBootstrapPendingDirectory, setNewSessionDraftTarget]);
 
     const handleConfirmDelete = React.useCallback(async () => {
         if (!deleteDialog) {