Support nested agent directories and add game-development category

- Add game-development to AGENT_DIRS in convert.sh, lint-agents.sh,
  install.sh, and the CI workflow
- Remove maxdepth 1 from find commands so nested subdirectories
  (e.g., game-development/unity/) are discovered
- Update CI git diff globs to **/*.md for recursive matching
- Remove strategy from lint AGENT_DIRS (playbooks, not agents)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/lint-agents.yml

@@ -5,6 +5,7 @@ on:
     paths:
       - 'design/**'
       - 'engineering/**'
+      - 'game-development/**'
       - 'marketing/**'
       - 'paid-media/**'
       - 'product/**'
@@ -28,9 +29,9 @@ jobs:
         id: changed
         run: |
           FILES=$(git diff --name-only --diff-filter=ACMR origin/${{ github.base_ref }}...HEAD -- \
-            'design/*.md' 'engineering/*.md' 'marketing/*.md' 'paid-media/*.md' 'product/*.md' \
-            'project-management/*.md' 'testing/*.md' 'support/*.md' \
-            'spatial-computing/*.md' 'specialized/*.md' 'strategy/*.md')
+            'design/**/*.md' 'engineering/**/*.md' 'game-development/**/*.md' 'marketing/**/*.md' 'paid-media/**/*.md' 'product/**/*.md' \
+            'project-management/**/*.md' 'testing/**/*.md' 'support/**/*.md' \
+            'spatial-computing/**/*.md' 'specialized/**/*.md' 'strategy/**/*.md')
           {
             echo "files<<ENDOFLIST"
             echo "$FILES"