Blender 5.0 compat + STB XML import + sequence/stamps improvements

- Fix Blender 5.0 API: active_sequence_strip → active_strip, bracket
  property access on AddonPreferences, _RestrictContext during register()
- Fix new_effect() frame_end → length for Blender 5.0
- Fix OTIO adapter kwargs (rate/ignore_timecode_mismatch only for cmx_3600)
- Fix OTIO global_start_time RationalTime → int conversion
- Add Import STB XML operator with movie strip import and XML patching
  for Storyboard Pro transitions missing <alignment>
- Add Create Sequence Strip operator (select shots → create sequence)
- Improve Set Stamps: channel at top, no conflict with existing strips,
  use raw strip names in templates
- TVSHOW episode fixes: sequence loading, episode creation
- Kitsu: new_asset, new_episode, admin_connect fix, gazu version pin
- Fix escape warnings in file_utils regex patterns
- Guard handler registration against duplicates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

__init__.py

@@ -36,28 +36,34 @@ import bpy
 
 
 def register():
-    bpy.app.handlers.frame_change_post.append(update_text_strips)
-    bpy.app.handlers.render_pre.append(update_text_strips)
+    if update_text_strips not in bpy.app.handlers.frame_change_post:
+        bpy.app.handlers.frame_change_post.append(update_text_strips)
+    if update_text_strips not in bpy.app.handlers.render_pre:
+        bpy.app.handlers.render_pre.append(update_text_strips)
 
     for module in modules:
         module.register()
 
-    bpy.app.handlers.frame_change_post.append(set_active_strip)
+    if set_active_strip not in bpy.app.handlers.frame_change_post:
+        bpy.app.handlers.frame_change_post.append(set_active_strip)
 
     prefs = get_addon_prefs()
     #print('\n\n-------------------', prefs.config_path)
 
 
 def unregister():
-    bpy.app.handlers.frame_change_post.remove(update_text_strips)
-    bpy.app.handlers.render_pre.remove(update_text_strips)
+    if update_text_strips in bpy.app.handlers.frame_change_post:
+        bpy.app.handlers.frame_change_post.remove(update_text_strips)
+    if update_text_strips in bpy.app.handlers.render_pre:
+        bpy.app.handlers.render_pre.remove(update_text_strips)
 
     try:
         bpy.utils.previews.remove(ASSET_PREVIEWS)
     except Exception as e:
         pass
 
-    bpy.app.handlers.frame_change_post.remove(set_active_strip)
+    if set_active_strip in bpy.app.handlers.frame_change_post:
+        bpy.app.handlers.frame_change_post.remove(set_active_strip)
     for module in reversed(modules):
         module.unregister()