fix: Add missing matcher fields to hooks.json files

Stop hooks (and other hook types) were not firing because they were
missing the required "matcher" field. According to the hook development
documentation, all hooks must have a matcher field - "*" for wildcard
matching.

Changes:
- Add matcher: "*" to all hooks in hookify, ralph-wiggum,
  explanatory-output-style, and learning-output-style plugins
- Update validate-hook-schema.sh to properly handle plugin format
  (with 'hooks' wrapper) vs settings format (events at root)
- Add validate-all-hooks.sh script to validate all hooks.json files

Fixes: https://anthropic.slack.com/archives/C08EHE6JF3L/p1765822035850959

plugins/learning-output-style/hooks/hooks.json

@@ -3,6 +3,7 @@
   "hooks": {
     "SessionStart": [
       {
+        "matcher": "*",
         "hooks": [
           {
             "type": "command",