upgrade: adopt V8.32.0-dev.1 (theme preview iframe fix, editor simple mode)

Overlay 46 upstream items; full patch set re-applied (all patched files
reset by overlay regardless of upstream change status — lesson recorded).
Verified: theme suites 35/35; dual-baseline 418 passed vs pristine
389+29 ours, FAILED-set diff EMPTY (same 10 Windows env fails).
Live: container 8.32.0-dev.1 healthy, hesupipe 192 entries intact,
trade-pro build 203 pages 0 errors.

Co-Authored-By: Claude Code <noreply@anthropic.com>

app/core.py

@@ -18,7 +18,6 @@ def discover_themes():
         raise RuntimeError(f'themes directory missing: {themes_dir}')
     found = []
     for entry in sorted(themes_dir.iterdir()):
-        # Underscore prefix marks non-theme assets (e.g. _professional_components.html).
         if not entry.is_dir() or entry.name.startswith('_'):
             continue
         try: