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

.gitignore

@@ -25,5 +25,8 @@ wavs
 .DS_Store
 Thumbs.db
 
+# JS dependencies
+web/ui/node_modules/
+
 # Temp
 /tmp/