feat: single-source theme discovery replaces three hardcoded whitelists

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

app/theme_pro.py

@@ -13,9 +13,8 @@ from pathlib import Path
 from urllib.parse import quote
 from jinja2 import Environment, FileSystemLoader, select_autoescape
 from markupsafe import Markup
-from .core import sanitize, route_path
+from .core import sanitize, route_path, THEMES
 
-THEMES=('automotive','industrial','corporate','minimal')
 ROOT=Path(__file__).resolve().parent.parent
 LOADER=Environment(loader=FileSystemLoader(str(ROOT/'themes')),autoescape=select_autoescape(['html','xml']))