fix(a11y): wrap matrix DialogTitle in Radix VisuallyHidden

[build-with-dhiraj]

What & why

A11y-only hardening of the shared matrix Dialog primitive (src/components/ui/Dialog.tsx) used by the three Skills-matrix modals (Gap / Capture / Export).

Radix's DialogContent warns when it cannot find its DialogTitle in the DOM (document.getElementById(titleId)), pointing you to wrap a hidden title with its VisuallyHidden component. This PR adopts that exact recommended pattern, replacing the project-sr-only-classed Title with Radix's own VisuallyHidden:

-<RadixDialog.Title className="sr-only">{label}</RadixDialog.Title>
+<VisuallyHidden asChild>
+  <RadixDialog.Title>{label}</RadixDialog.Title>
+</VisuallyHidden>

The Title stays visually hidden (renders 1x1, clipped) so there is zero layout or behavior change. This makes the accessible name robust regardless of how the project's sr-only utility is defined now or in the future, which is the canonical Radix guidance.

Changes

• src/components/ui/Dialog.tsx — use VisuallyHidden asChild around RadixDialog.Title; updated the doc comment to match.
• package.json / package-lock.json — add @radix-ui/react-visually-hidden as a direct dependency (it was already present transitively via @radix-ui/react-dialog).

No other files touched. src/lib/labs/mcclean.ts untouched. Zero em-dashes. joVE | LabOS design system preserved.

Verification (empirical, in-browser)

Ran the app locally and opened each of the three modals via the real triggers (coverage-gap cell, "Launch tacit capture", and Compliance-on -> "Form 483 audit export").

Modal	Console (errors/warnings)	Accessible name	Focus in	Escape closes + focus restores	Layout
Gap (Create onboarding plan)	0 / 0	present (VisuallyHidden Title)	yes (Close)	yes -> restored to gap cell	unchanged
Capture (Tacit knowledge capture)	0 / 0	present	yes (Close capture)	yes -> restored to launch button	unchanged
Export (Form 483 audit export)	0 / 0	present	yes (Close export)	yes -> restored to export button	unchanged (visible h2 still 316x24)

The VisuallyHidden Title renders at 1x1 (clipped) and the dialog's aria-labelledby resolves to it, so screen-reader users get the name while sighted layout is identical.

CI parity (local)

• tsc --noEmit clean
• lint: no lint script (CI skips it, matching main)
• next build succeeds (all 9 static pages generated)
• npm ci --dry-run confirms lockfile in sync

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