fix(gui): drop stale from src.command_palette import in render_main_interface

The REAL cause of the "black window" bug. The render_main_interface
function (in App._gui_func every frame) was importing render_palette_modal
from `src.command_palette`, a module that was DELETED in
`module_taxonomy_refactor_20260627` (the refactor moved the registry into
`src/commands.py` but `render_palette_modal` itself is a render function
in `src/gui_2.py` because it owns ImGui state).

Every frame, this local import raised ModuleNotFoundError. The error was
silently caught by `_render_main_interface_result`'s outer try/except
(Result-based error drain), so the entire `render_main_interface` body
was aborted. That meant `_render_window_if_open(...)` was never called
for ANY window, and the dockspace was never populated with the
8 default-visible windows. Hence the user-visible "only menu ribbon
showing" symptom.

Two-part fix:

1. Removed the broken local imports inside render_main_interface:
   - `from src.command_palette import render_palette_modal` (deleted module)
   - `from src.commands        import registry as _cmd_registry` (local import anti-pattern per python.md §17.9a)

2. Extended the existing top-level command-palette imports block in
   src/gui_2.py (line 8772) to add `registry as _cmd_registry`:
   `from src.commands import Command as _CpCommand, fuzzy_match as
    _cp_fuzzy_match, _close_palette, _execute as _cp_execute,
    registry as _cmd_registry`

3. Replaced the local-import block with a direct call:
   `render_palette_modal(app, _cmd_registry.all())`

`render_palette_modal` is defined locally in src/gui_2.py at line 8775
(it owns ImGui state per the comment in src/commands.py:21), so the call
is a direct function reference. `registry` is now imported once at the
top of the file, eliminating the function-level import.

The `from src.commands import ...` block at line 8772 was already top-level
so adding `registry as _cmd_registry` to it is a single-line extension
(no new import statement).

Why the existing test suite didn't catch this:
- `test_commands_does_not_import_gui_2_at_module_level` checks MODULE-LEVEL
  imports, not function-level local imports
- The function-level `from src.command_palette import render_palette_modal`
  is a python.md §17.9a banned pattern (Local imports inside functions)
  but the §17.9a audit (audit_imports.py with whitelist) had this
  file in the hot-reload whitelist
- The 3 install tests + 14 adjacent tests all run in subprocess.Popen
  shells that have a SHORT lifetime (~5s); the ModuleNotFoundError
  doesn't cause the subprocess to crash, it just makes render_main_interface
  no-op every frame. Tests that read INI content or app.show_windows
  state don't notice the rendering is broken.

Empirical verification (manual launch 18s with --enable-test-hooks OFF):
- Before fix: stderr shows 50+ "[FATAL] render_main_interface crashed:
  ModuleNotFoundError: No module named 'src.command_palette'" lines
  (one per frame at 60fps for 8 seconds)
- After fix: stderr shows ZERO FATAL lines; saved INI contains 8
  [Window][X] entries + [Docking][Data] + 2 DockNode children +
  0 stale window names
- 17/17 tests still pass (3 install + 2 reset_layout + 8 gui + 4 commands)
- Reverted the diagnostic stderr writes I added in _render_window_if_open
  and _render_main_interface_result during investigation; both back to
  their pre-debug state

src/gui_2.py

@@ -1893,8 +1893,6 @@ def render_main_interface(app: App) -> None:
  render_save_preset_modal(app)
  render_save_workspace_profile_modal(app)
  render_add_context_files_modal(app)
- from src.command_palette import render_palette_modal
- from src.commands        import registry as _cmd_registry
  render_palette_modal(app, _cmd_registry.all())
  render_preset_manager_window(app)
  render_tool_preset_manager_window(app)
@@ -8757,7 +8755,7 @@ def draw_soft_shadow(draw_list: imgui.ImDrawList, p_min: imgui.ImVec2, p_max: im
 #endregion: Shaders
 
 #region: Command Palette Modal (rendering only; registry lives in src/commands.py)
-from src.commands import Command as _CpCommand, fuzzy_match as _cp_fuzzy_match, _close_palette, _execute as _cp_execute
+from src.commands import Command as _CpCommand, fuzzy_match as _cp_fuzzy_match, _close_palette, _execute as _cp_execute, registry as _cmd_registry
 
 def render_palette_modal(app: Any, commands: List[Any]) -> None:
  if not getattr(app, "show_command_palette", False):