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>

operators/spreadsheet.py

@@ -341,7 +341,7 @@ class VSETB_OT_import_spreadsheet(Operator):
         settings = get_scene_settings()
         project = settings.active_project
         spreadsheet = project.spreadsheet_import
-        sequencer = scn.sequence_editor.sequences
+        sequencer = scn.sequence_editor.strips
 
         assets_missing = set()
 
@@ -397,7 +397,7 @@ class VSETB_OT_import_spreadsheet(Operator):
                         type='COLOR',
                         channel=channel,
                         frame_start=frame_start,
-                        frame_end=frame_end,
+                        length=frame_end - frame_start,
                     )
 
                 strip.blend_alpha = 0.0