fix: resolve all 14 ESLint warnings across the codebase

- Add varsIgnorePattern to no-unused-vars for destructuring patterns
- Fix all react-hooks/exhaustive-deps by adding missing dependencies
- Refactor useAnimatedNumber to use ref instead of stale state closure
- Wrap handleLinkResult in useCallback for stable deps
- Extract OAuth utilities from OAuthCallback.tsx to utils/oauth.ts
- Extract background config utilities to utils/backgroundConfig.ts
- Remove unused catch parameter in GiftSubscription

src/pages/GiftSubscription.tsx

@@ -611,7 +611,7 @@ function BuyTabContent({
               setSubmitError(t('gift.failedDesc'));
             }
             // 'cancelled' — user closed the invoice, do nothing
-          } catch (e) {
+          } catch {
             setSubmitError(t('gift.failedDesc'));
           }
           return;