Add UA override for chzzk.naver.com, update manifest/UI, and add CI build workflow

[emptycan1010]

Motivation

• Some requests to https://chzzk.naver.com/* require a specific User-Agent to behave correctly, so the extension should be able to override the browser User-Agent when accessing that host.
• The UA override should be configurable by users and persist via existing options infrastructure.
• Ensure builds and linting run automatically by adding a CI workflow for push and pull request events.

Description

• Added a boolean option uaChange to src/types/options.ts with a default of true and exposed it in the popup UI by adding a new option checkbox in src/entrypoints/popup/App.tsx.
• Implemented dynamic declarativeNetRequest rule management in src/entrypoints/background.ts with setChzzkUserAgentRule, and wired syncing on startup/installation and on option changes using chrome.storage.onChanged and getOption.
• Updated wxt.config.ts to include the declarativeNetRequest permission and host_permissions for https://chzzk.naver.com/* so the rule can be applied.
• Added a GitHub Actions workflow (.github/workflows/build.yml) that checks out the repo, sets up pnpm and Node.js, installs dependencies, runs pnpm eslint ., and runs pnpm build, and uploads the Chrome build artifact.

Testing

• A CI job was added to run pnpm install --frozen-lockfile, pnpm eslint ., and pnpm build on push and pull request events, but no CI run results are included in this change.
• No automated test failures are reported in this rollout; local type-checking and build steps are expected to be covered by the added workflow.

---

Codex Task