Corrects the source-input aria-label wording to match the UIUX Cycle 4
spec exactly. Previous commit used "Install plugin from source URL";
spec says "Install from source URL" (matches the visible "Install from
source" section heading). Updates the corresponding test assertions.
No functional change. All 736 tests pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>