cleanup and rename provider to plugin

docs/PR_PLUGIN_AUTHORING.md

@@ -0,0 +1,15 @@
+PR Title: docs: Add plugin authoring doc, examples, and tests
+
+Summary:
+- Add `docs/plugin_authoring.md` describing the strict `ResultModel`-based plugin adapter pattern, `ColumnSpec` usage, `selection_fn`, and `TablePluginMixin` for HTML table scraping.
+- Link the new doc from `docs/result_table.md`.
+- Add plugin-author example coverage to validate the example plugin integration with the registry.
+
+Why:
+- Provide a short, focused Quick Start to help contributors author plugins that integrate with the strict ResultTable API.
+
+Testing:
+- New tests pass locally (plugin-related subset).
+
+Notes:
+- The change is documentation-first and non-functional, with tests ensuring examples remain valid.