fix: add markdownlint config and auto-fix markdown errors

- Add .markdownlint-cli2.jsonc based on headlamp-agent-skills config
- Disable MD013 (line length), MD041 (first-line-heading), MD036
  (emphasis-as-heading), MD024 (no-duplicate-heading), MD040
  (fenced-code-language), MD060 (table-column-style), MD029
  (ol-prefix), MD033 (no-inline-html) — appropriate for plugin docs
- Run markdownlint-cli2 --fix to auto-fix MD022, MD031, MD032
- Manually fix remaining code block language annotations

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.markdownlint-cli2.jsonc

@@ -0,0 +1,20 @@
+{
+  "config": {
+    // Line length — not enforced for docs with code examples
+    "MD013": false,
+    // First line heading — files use YAML frontmatter, not headings
+    "MD041": false,
+    // Emphasis as heading — common pattern for Option 1/2/3 sections
+    "MD036": false,
+    // No duplicate heading — changelog files repeat section names intentionally
+    "MD024": false,
+    // Fenced code language — not always applicable for diagram blocks
+    "MD040": false,
+    // Table column style — table alignment is visual, not semantic
+    "MD060": false,
+    // Ordered list item prefix — number resets are intentional in documents
+    "MD029": false,
+    // No inline HTML — each elements are valid in valid Markdown
+    "MD033": false
+  }
+}