chore: add .gitignore for node_modules, dist, coverage, .codegraph

The repo had no .gitignore, leaving build/dependency artifacts untracked
but committable. Ignore them to prevent accidental commits.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: casabre

.gitignore

@@ -0,0 +1,16 @@
+# Dependencies
+node_modules/
+
+# Build output
+dist/
+
+# Test / coverage artifacts
+coverage/
+
+# CodeGraph index
+.codegraph/
+
+# Env / local
+.env
+.env.local
+*.log