feat(playground): replace native title attributes with v0 Tooltip

[sridhar-3009]

Fixes #495 (playground half — apps/docs was already migrated in #621).

Summary

Native title= tooltips don't work well for keyboard focus, touch, or screen readers. #621 introduced AppTooltip and migrated apps/docs to it, but apps/playground was never covered — six files still had native title= attributes, and PlaygroundAppBar.vue had two spots already migrated to AppTooltip alongside one that was missed.

What changed

• AppIconButton.vue: deleted. Its only consumer (AppThemeToggle) was wrapping a button-rendering component inside another button-rendering AppTooltip activator, which would nest two interactive elements. Moved the icon markup directly into AppThemeToggle instead, matching how AppCloseButton (already migrated in apps/docs) wraps plain SVG/icon content rather than another button component.
• AppThemeToggle.vue: wraps the icon directly in AppTooltip.
• AppCloseButton.vue: same shape as the already-migrated apps/docs copy, including making the .close-button style block unscoped (AppTooltip renders a multi-root fragment, so a scoped selector wouldn't match the rendered button — see feat(genesis): add GnActionButton action-button primitive #359).
• PlaygroundAppBar.vue: converts the one remaining native-title button (Switch to preview/editor) to AppTooltip, matching the two siblings in the same file that were already migrated.
• PlaygroundMenuBar.vue: the Menu trigger is a Popover.Activator, not a plain button — wrapping it in another trigger component would nest two overlay activators. Replaced title="Menu" with aria-label="Menu" instead of forcing AppTooltip onto it.
• PlaygroundEditorFileTree.vue: converts all four toolbar buttons (New file, New folder, Toggle config files, Delete) to AppTooltip, keeping each existing aria-label (static or dynamic) alongside the new text prop.

No changes to main.ts — neither apps/docs nor apps/playground installs createTooltipPlugin, so no plugin registration is needed; AppTooltip sets its own openDelay/closeDelay defaults.

Rebase note

This PR previously used the raw Tooltip.Root/Tooltip.Activator/Tooltip.Content pattern from before AppTooltip existed, and had drifted into merge conflicts. Fully rewrote it against current master to use AppTooltip — the same wrapper apps/docs already uses — rather than reintroducing a pattern AppTooltip was specifically created to replace.

Testing

• pnpm lint — clean
• pnpm typecheck — clean
• pnpm build:play (client + SSR build, page rendering) — succeeds
• pnpm repo:check (knip + sherif) — no issues, confirming AppIconButton's removal didn't leave any dangling references

All four checks run from a clean worktree of this exact commit (fresh pnpm install), not just my local working copy.

[johnleider]

This PR currently has merge conflicts with its base branch (master) and can't be merged as-is. Could you rebase onto the latest master and resolve the conflicts when you get a chance?

Context: we're adopting a git-flow branch model — master for fixes/patches, dev for features (minor), next for breaking changes (major). This PR is correctly targeting master; it just needs a rebase to clear the conflicts. Thanks!