[yr75myjnqx-tech]

Problem

On boxes that are expected to run their unified memory tight (e.g. a GB10 serving an FP4 model that intentionally holds ~93 of 121 GB), the Overview page shows a persistent "Unified memory is running low — 2.7 GB available" strip row. The condition is by-design, so the alert is noise — but the row can't be cleared, and it sits at the top of the Overview indefinitely.

Change

Adds a small x dismiss button to each FleetAlertStrip row:

• Session-only dismissal — component state, deliberately not persisted. A page refresh restores the warning, so nothing can be permanently silenced and a fresh session re-surfaces the condition.
• Re-fire aware — dismissed keys are pruned whenever the underlying condition is no longer active, so if the alert clears and later fires again, the row reappears without a refresh.
• Throttle alerts are not dismissible — they're treated as safety-relevant elsewhere in this component (showExceptions filtering), so the x is omitted for them.
• The existing Open button remains the row's first button, so existing keyboard/automation flows that target the primary action are unchanged.
• New overview:alerts.dismiss i18n key (en + zh-CN) and .ov-alert__dismiss styles (24px hit target, muted color, hover state).

Tests

• 4 new cases in FleetAlertStrip.test.tsx: dismiss hides the row; remount (refresh) restores it; clear-then-refire restores it without a refresh; throttle rows render no dismiss button.
• FleetAlertStrip.test.tsx: 11/11 passing. Full suite: 900/900 tests passing.
• Note: 10 test files fail to collect on a clean upstream/main checkout (missing src/shared/mainFilesystem imported by SparkCard.tsx) — pre-existing on main, unrelated to this PR; the same files fail identically with and without this change.