fix(frontend): restore notification sound and browser tab flash on agent completion (#14049)

Co-authored-by: openhands <openhands@all-hands.dev>

.agents/skills/custom-codereview-guide.md

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+---
+name: custom-codereview-guide
+description: Repo-specific code review guidelines for All-Hands-AI/OpenHands. Provides frontend and backend review rules in addition to the default code review skill.
+triggers:
+- /codereview
+---
+
+# All-Hands-AI/OpenHands Code Review Guidelines
+
+You are an expert code reviewer for the **All-Hands-AI/OpenHands** repository. This skill provides repo-specific review guidelines.
+
+## Frontend: i18n / Translation Key Usage
+
+**Never dynamically construct i18n keys via string interpolation or template literals.**
+
+All translation keys must come from the `I18nKey` enum (`frontend/src/i18n/declaration.ts`) or from canonical mapping objects like `AGENT_STATUS_MAP` (`frontend/src/utils/status.ts`). Dynamically constructed keys (e.g., `` t(`STATUS$${value.toUpperCase()}`) ``) will silently fall back to the raw key string at runtime because `i18next` returns the key itself when a translation is missing — this produces broken UI text with no build-time or test-time error.
+
+### What to flag
+
+- Any call to `t(...)` or `i18next.t(...)` where the key is built at runtime via template literals, string concatenation, or helper functions rather than referencing `I18nKey` or a known mapping
+- Any new i18n key referenced in code that does not exist in `frontend/src/i18n/translation.json`
+
+### Correct pattern
+
+```ts
+import { AGENT_STATUS_MAP } from "#/utils/status";
+
+const i18nKey = AGENT_STATUS_MAP[agentState];
+const message = i18nKey ? t(i18nKey) : fallback;
+```
+
+### Incorrect pattern
+
+```ts
+// BAD: constructs a key that may not exist in translation.json
+const message = t(`STATUS$${agentState.toUpperCase()}`);
+```
+
+## Frontend: Data Fetching Architecture
+
+UI components must never call API client methods (`frontend/src/api/`) directly. All data access must go through TanStack Query hooks:
+
+```
+UI components → TanStack Query hooks (frontend/src/hooks/query/ or mutation/) → API client (frontend/src/api/) → API endpoints
+```
+
+Flag any component that imports directly from `#/api/` and calls fetch/mutation functions without a TanStack Query wrapper.