test(NotAvailablePanel, AttachmentViews): add 19-case vitest suites
Add vitest coverage for two remaining chat/FilesTab components:
- NotAvailablePanel: 5 cases — heading, monospace runtime name, helper
text, SVG aria-hidden, different runtime display
- AttachmentViews (PendingAttachmentPill + AttachmentChip): 14 cases —
file name/size rendering, formatSize units, remove/download callbacks,
aria-labels, tone styles, SVG glyph
Fix: use Object.defineProperty to override jsdom File size (jsdom
ignores the size constructor arg); use afterEach(cleanup) to prevent
accumulated DOM elements between NotAvailablePanel tests.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>