chore: add graphify hooks, CLAUDE.md, and gitignore updates

- .claude/settings.json: PreToolUse hooks redirecting grep/file reads
  to graphify query when graph.json exists
- CLAUDE.md: graphify knowledge graph instructions for Claude Code sessions
- .gitignore: exclude graphify-out/ and .claude/settings.local.json
- .vscode/extensions.json: add comments header

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

.vscode/extensions.json

@@ -1,4 +1,6 @@
 {
+    // See http://go.microsoft.com/fwlink/?LinkId=827846
+    // for the documentation about the extensions.json format
     "recommendations": [
         "pioarduino.pioarduino-ide",
         "platformio.platformio-ide"