MDS060: declare markdownlint frontmatter rules

The rule-readme schema (internal/rules/proto.md) now requires
each README to list the markdownlint rule(s) it covers, so
MDS020 can validate the coverage matrix from front matter
instead of free-form prose.

https://claude.ai/code/session_012X1wVbY7u9DNMpGRhNurzT

Author: claude

internal/rules/MDS060-table-structure/README.md

@@ -9,6 +9,13 @@ description: >-
 nature: style
 category: table
 maintainability: null
+markdownlint:
+  - id: MD055
+    name: table-pipe-style
+  - id: MD056
+    name: table-column-count
+  - id: MD058
+    name: blanks-around-tables
 ---
 # MDS060: table-structure