fix: revert regression -- restore working markdownlint ignores config

A later commit on this branch (1ccca81, applying orama PR #320 review
4837623699) replaced the working ignores-based MD013 exemption with the
overrides/filter/combine schema already proven this session not to work
against CI's actually-pinned markdownlint-cli2 v0.17.2 -- reintroducing
the exact CI failure that had already been diagnosed and fixed.

Restored the ignores-based config, verified against the exact CI-pinned
tool version (markdownlint-cli2 v0.17.2, not the newer local default):
SKILL.md, docs/LESSONS.md, and .agent/memory/semantic/DECISIONS.md all
correctly exempted, 0 issues.

29/29 tests pass. Hygiene clean.

Author: diazMelgarejo

.markdownlint-cli2.jsonc

@@ -11,17 +11,9 @@
       "stern": false
     }
   },
-  "overrides": [
-    {
-      "filter": [
-        "SKILL.md",
-        "**/SKILL.md",
-        "**/skills/**"
-      ],
-      "config": {
-        "MD013": false
-      },
-      "combine": "merge"
-    }
+  "ignores": [
+    "**/SKILL.md",
+    "**/LESSONS.md",
+    "**/DECISIONS.md"
   ]
 }