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>

file_utils.py

@@ -54,7 +54,7 @@ def norm_str(string, separator='_', format=str.lower, padding=0):
     string = string.replace('_', ' ')
     string = string.replace('-', ' ')
     string = re.sub('[ ]+', ' ', string)
-    string = re.sub('[ ]+\/[ ]+', '/', string)
+    string = re.sub(r'[ ]+/[ ]+', '/', string)
     string = string.strip()
 
     if format:
@@ -74,7 +74,7 @@ def norm_name(string, separator='_', format=str.lower, padding=0):
     string = string.replace('_', ' ')
     string = string.replace('-', ' ')
     string = re.sub('[ ]+', ' ', string)
-    string = re.sub('[ ]+\/[ ]+', '/', string)
+    string = re.sub(r'[ ]+/[ ]+', '/', string)
     string = string.strip()
 
     if format: