chore: add JS/ESLint toolchain, refactor onclick to event delegation

- Add ESLint config for web/ui (flat config, golangci-lint-compatible)
- Add js-lint task to mise.toml (npm run lint in web/ui)
- Add ESLint check to check-toolchain.sh
- Add .golangci.yml for golangci-lint v2 with correct exclusions
- Refactor app.js: replace inline onclick with data-action + event delegation
- Add null checks and HTTP status checks to browseWavs
- Add web/ui/node_modules/ to .gitignore

scripts/check-toolchain.sh

@@ -123,5 +123,16 @@ else
     fi
 fi
 
+echo ""
+echo "=== JS Linting (ESLint) ==="
+if [ -f web/ui/node_modules/.bin/eslint ]; then
+    ok "ESLint installed at web/ui/node_modules/.bin/eslint"
+    eslint_ver=$(cd web/ui && ./node_modules/.bin/eslint --version 2>/dev/null)
+    ok "ESLint: $eslint_ver"
+else
+    warn "ESLint not installed (needed for web UI linting)"
+    echo "    Install: cd web/ui && npm install"
+fi
+
 echo ""
 echo "=== Core toolchain check complete ==="