Make a container action tell the truth about what happened

The response was discarded, so a refused stop looked like a completed one, and the payload the
card redraws from is cached for 300s with no invalidation — the container carried on showing as
running until the once-a-minute writer caught up. Stop now confirms; start still does not.

Plugin/unraid/include/config.php

@@ -456,6 +456,17 @@ function vv_cache_write(string $key, array $data): void {
     rename($tmp, $f);
 }
 
+// Drop a cached payload so the next read collects fresh. For use by endpoints that change the
+// very state a cache describes: without it the UI polls a payload that cannot yet know about the
+// action it just took, and the operator sees a container they stopped still running until the
+// background writer next comes round.
+//
+// Best-effort by design. A cache that could not be removed is a stale read, which is what would
+// have happened anyway — never a reason to fail the action that was actually requested.
+function vv_cache_clear(string $key): void {
+    @unlink(VV_CACHE_DIR . '/' . $key . '.json');
+}
+
 // ── Shared utility functions (used across include/ and api/ files) ────────────
 
 // Format seconds into "2d 3h 15m".