fix: Resolve dead links in documentation files

- 02-memory/README.md: Remove broken example links, keep valid ones
- CONTRIBUTING.md: Fix relative path to SECURITY.md
- 07-plugins/README.md: Update MCP spec URL to working domain
- .github/SECURITY_REPORTING.md: Update OWASP link to valid cheatsheet
- .github/ISSUE_TEMPLATE/*: Replace placeholder links with comments
- .github/markdown-link-check-config.json: Add ignore patterns for
  example URLs in code blocks (docs.example.com, template files)

.github/markdown-link-check-config.json

@@ -1,5 +1,21 @@
 {
   "ignorePatterns": [
+    {
+      "pattern": "^https://docs\\.example\\.com",
+      "comment": "Example placeholder URLs in documentation templates"
+    },
+    {
+      "pattern": "^\\./docs/",
+      "comment": "Example relative paths in documentation templates"
+    },
+    {
+      "pattern": "^FORMS\\.md$|^REFERENCE\\.md$",
+      "comment": "Example file references in skill templates"
+    },
+    {
+      "pattern": "^https://en\\.wikipedia\\.org/wiki/N%2B1",
+      "comment": "Wikipedia N+1 article - URL encoding issues"
+    },
     {
       "pattern": "^https://twitter.com",
       "comment": "Twitter/X links require authentication"