refactor(web-ui): migrate exclusive switchers, menus, toolbar, and tooltips onto @bitfun/ui

[kev1n77]

Summary

Adopt the remaining high-value @bitfun/ui primitives in Web UI chrome, and add the missing Tooltip primitive to the design system.

• Replace custom exclusive switchers with SegmentedControl (Git diff type, Markdown editor view mode, font-size presets).
• Replace hand-rolled dropdowns with Menu / MenuItem / MenuSection / MenuSeparator (market account, workspace item, assistant-session create, MiniApp gallery import, nav footer settings, MainNav workspace switcher, ShellNav workspace switcher).
• Rebuild the image-viewer header on Toolbar / ToolbarGroup / ToolbarSeparator.
• Add ActionItem tone="danger" so destructive menu rows share the status-danger tokens.
• Add @bitfun/ui Tooltip + TooltipProvider (placement flip, follow-cursor, interactive persistence, overlay.tooltip tokens) and switch product surfaces outside flow_chat to it.

Retire the corresponding appearance parts and migrate persisted appearance packages. flow_chat and leftover legacy Tooltip internals are intentionally unchanged.

Fixes #

Type and Areas

Type:

Feature / UI/UX / refactor

Areas:

web UI, design system (@bitfun/ui, @bitfun/design-tokens, Design Lab), appearance migration

Motivation / Impact

Product chrome still mixed design-system primitives with one-off buttons, popovers, and the legacy @/component-library Tooltip. That duplicated overlay chrome, appearance parts, and styling, and left Menu / Toolbar / Tooltip unused in the places they were built for.

After this change:

• Exclusive two/three-option switchers, nav/settings/workspace dropdowns, the image-viewer toolbar, and most product tooltips render from @bitfun/ui.
• Destructive menu rows (close / delete / reset) use a shared danger tone instead of ad-hoc red styles.
• Older appearance packages that still reference retired parts (levelGroup, modeToggle, footerMenu, workspaceMenu, image-viewer toolbar parts, etc.) migrate automatically.
• Design Lab can preview Tooltip placements.

No change to Agent Runtime, remote workspace, peer-device, or detached-dispatch behavior. flow_chat still uses the legacy Tooltip.

Verification

pnpm run design-system:build
pnpm run design-system:test
pnpm run design-system:check
pnpm -w run type-check:web
pnpm exec vitest run
pnpm -w run check:web
pnpm run theme:color-audit:all

pnpm exec vitest run was run from src/web-ui and passed 568 files / 4110 tests.

Local-only UI chrome. Not exercised in remote workspace, remote control, Peer Device Mode, or Detached Dispatch.

Manual checks in desktop:dev:

• Git DiffView Working Tree / Staged switcher
• Markdown editor source / preview toggle
• Appearance font size presets
• Nav footer settings menu, MainNav workspace menu, workspace-item menus, MiniApp import menu
• Image viewer zoom / rotate / close toolbar
• Hover tooltips on nav, settings, and SSH dialogs (not flow_chat)

Reviewer Notes

• Commits are already split by primitive: SegmentedControl, Menu (3 batches), Toolbar, ActionItem tone, then Tooltip (design system + web-ui).
• Overlay contract: portals that render @bitfun/ui Menu, Modal, or ConfirmDialog own their chrome. overlay-surfaces.contract.test.ts accepts that instead of requiring floating-surface or dialog-surface mixins.
• Tooltip portals go through TooltipProvider with portalContainer={getAppearanceOverlayHost} in App.tsx, matching Modal.
• Custom tooltip width overrides now target [data-bf-part='content'] and clear max-inline-size where the 280px cap would clip Agent capability / Create Agent copy.
• Do not delete the legacy Tooltip yet. flow_chat and a few component-library internals still import it.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.