feat(tree-sitter, views): initialize AST on focus and emit source view creation event

- Add set_ast helper to centralize Tree-sitter parsing logic
- Parse and attach AST on FocusedViewEvent and TextChangedEvent
- Request file from buffer on view focus before parsing
- Fix parser guard condition in get_parser (handle missing language properly)

- Emit CreatedSourceViewEvent when a new source view is added
- Register CreatedSourceViewEvent in DTO exports

- Update TODO:
  - Remove completed collapsible code blocks task
  - Add fix note for code block icon desync issue

chore:
- Add scaffolding for code_fold UI plugin
- Add created_source_view_event DTO

plugins/code/ui/code_fold/folding_actions.py

@@ -0,0 +1,22 @@
+# Python imports
+
+# Lib imports
+
+# Application imports
+
+
+
+def collapse_range(view, fold):
+    buffer = view.get_buffer()
+    start  = buffer.get_iter_at_line(fold["start_line"] + 1)
+    end    = buffer.get_iter_at_line(fold["end_line"] + 1)
+
+    buffer.apply_tag_by_name("invisible", start, end)
+
+
+def expand_range(view, fold):
+    buffer = view.get_buffer()
+    start  = buffer.get_iter_at_line(fold["start_line"] + 1)
+    end    = buffer.get_iter_at_line(fold["end_line"] + 1)
+
+    buffer.remove_tag_by_name("invisible", start, end)