fix(canvas): give the Add card picker a backdrop scrim (#872)

[h4yfans]

Summary

Fixes #872 — the canvas Add card picker rendered without a dimmed backdrop, so the canvas behind it stayed at full contrast and the dialog read as floating rather than modal.

Root cause: cmdk 1.1.1's Command.Dialog spreads className onto the cmdk root (inside Dialog.Content) and routes the Radix parts through separate overlayClassName / contentClassName props — confirmed in the shipped bundle:

React.createElement(Dialog.Overlay, { "cmdk-overlay": "", className: overlayClassName })

So the overlay was rendering with an empty className and nothing was styling it. The dialog was already functionally modal via Radix; this was purely visual.

The fix routes the scrim through overlayClassName with the same bg-black/50 the command palette uses. Positioning and DOM structure are untouched — Radix renders Overlay before Content, so the panel still paints above it.

Also on this branch:

• A red-first renderer test asserting [cmdk-overlay] carries the scrim class.
• One clause in apps/docs/src/user-guide/canvas/cards-and-links.md (the docs gate flagged the file): the picker opens over a dimmed canvas, Esc or outside-click dismisses. Both are existing Radix defaults, not new behavior.

Release note

The canvas "Add card" picker now dims the canvas behind it, matching the search palette.

Test plan

• vitest --project renderer canvas-add-card-dialog.test.tsx → PASS 12 / FAIL 0 (new test failed first with expected '' to contain 'bg-black/50')
• pnpm --filter @memry/desktop typecheck:web → clean
• eslint on both touched files → only pre-existing set-state-in-effect warnings on the untouched effects (lines 49–53, 65–68)
• prettier --check → clean
• pnpm docs:impact --base origin/main --strict → covered
• pnpm docs:build → complete

Not manually verified in the running app — the change is one Tailwind class on the Radix overlay, covered by the DOM assertion.

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[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit a304b8e.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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