Add headless regression tests for Phase 4b features

- Implement test for popup anchor behavior in rule-builder menus to ensure consistent anchor positioning during menu transitions.
- Create tests for stage logic, including mode transitions, toolbar visibility, and status bar updates.
- Add terrain drag-painting tests to verify correct block placement behavior and conflict handling.
- Introduce walk waypoint tests to check for arrival conditions and position stability after navigation.

docs/phase_3a_spec.md

@@ -543,7 +543,8 @@ if _direct_mode:
 - If `_pending_walk_target` and `_context_rig` valid → append
   `{"type":"walk_to","target":world_pos}` to `_context_rig`; clear pending + context.
 - Else `var hit := _selection.hit_test(world_pos)`; if `hit is STICKMAN_RIG` →
-  `_context_rig = hit`, position `_action_popup` at the mouse and `popup()`. Non-stickman
+  `_context_rig = hit`, position `_action_popup` to the **right of the clicked stickman**
+  (`_world_to_screen(hit.global_position)` + 24 px) and `popup()`. Non-stickman
   clicks are ignored.
 
 **Popup handler `_on_action_popup_id_pressed(id)`** (guards `_context_rig` valid):
@@ -657,7 +658,7 @@ Implementation notes:
 ## 7. UI flow (Milestone 3)
 
 1. Press **"Direct"** (toggle). Palette spawn modes are cleared (mutually exclusive).
-2. Click a stickman → `StageSelection.hit_test` → if stickman, open `_action_popup` at cursor.
+2. Click a stickman → `StageSelection.hit_test` → if stickman, open `_action_popup` to the right of the clicked stickman (its world position converted to screen + 24 px).
 3. Choose:
    - **Walk To** → enters pending mode; status hint ("Click stage for walk target — Esc to cancel").
    - **Speak** → text dialog → append `speak` action.