Continues the EditorLayout decomposition (B4-2). Pulls the inline
three-tab Create Stack dialog (Empty / From Git / From Docker Run) out
of EditorLayout into EditorLayout/CreateStackDialog.tsx.
Parent now owns only the open boolean and a domain callback pair;
all 14 form-state vars and 6 handlers move into the child. The slot
renders a thin trigger button plus the new dialog.
Metrics:
- EditorLayout.tsx: 3,266 -> 2,843 LOC
- new CreateStackDialog.tsx: 463 LOC (under the 500 ceiling)
- useState count in EditorLayout: 81 -> 66
Anso