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

mise.toml

@@ -11,7 +11,8 @@ build = "go build -buildvcs=false -o fetch ."
 akaiutil = "make -C third_party/akaiutil"
 all = { run = "go build -buildvcs=false -o fetch . && make -C third_party/akaiutil" }
 serve = { run = "go build -buildvcs=false -o fetch . && ./fetch serve" }
-lint = "go vet ./..."
+lint = "golangci-lint run"
+js-lint = "cd web/ui && npm run lint"
 electron-deps = "cd electron && npm install"
 electron-dev = { run = "go build -buildvcs=false -o fetch . && cd electron && npx electron ." }
 electron-build = { run = "go build -buildvcs=false -o fetch . && make -C third_party/akaiutil && cd electron && npx electron-builder --dir" }