refactor(web-ui): migrate product shell UI onto @bitfun/ui primitives

[kev1n77]

Summary

Adopt the remaining high-value @bitfun/ui primitives in the Web UI product shell, add the missing Tooltip primitive, and keep flow_chat frozen.

• 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 and switch product surfaces outside flow_chat to it.
• Replace remaining product viewports, labeled form stacks, scene navigation, and 1:1 lucide glyphs with ScrollArea, FieldGroup, NavigationPanel, and catalog Icons.
• Expose NavigationPanel bodyRef so sticky scene headers can track the same scroll root.

Retire the corresponding appearance parts and migrate persisted appearance packages.

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

The product shell still mixed design-system primitives with one-off buttons, popovers, scroll wrappers, scene navigation, and the legacy @/component-library Tooltip. That duplicated overlay surfaces, appearance parts, and icon/styling paths.

After this change:

• Exclusive switchers, nav/settings/workspace dropdowns, the image-viewer toolbar, most product tooltips, scroll viewports, settings form groups, and scene navigation rails render from @bitfun/ui.
• Destructive menu rows use a shared danger tone.
• Scene icons that match the catalog 1:1 come from @bitfun/ui Icons instead of raw lucide imports.
• Older appearance packages that still reference retired parts (levelGroup, modeToggle, footerMenu, workspaceMenu, sections on git/settings/nav, image-viewer toolbar parts, and others) migrate automatically.
• Design Lab can preview Tooltip placements.

No change to Agent Runtime, remote workspace, peer-device, or detached-dispatch behavior. flow_chat is unchanged.

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

Run pnpm exec vitest run from src/web-ui.

Local-only product-shell UI. 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)
• Settings / Git / File Viewer / Shell scene rails
• Scrollable settings pages, dialogs, and list viewports
• Grouped form stacks in SSH, relay deploy, and settings editors

Reviewer Notes

• Nine commits, already split by primitive: SegmentedControl, Menu (3 batches), Toolbar, ActionItem tone, Tooltip (design system + web-ui), then ScrollArea / FieldGroup / NavigationPanel / Icons.
• Overlay contract: portals that render @bitfun/ui Menu, Modal, or ConfirmDialog own their surface. 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.
• NavigationPanel bodyRef is a small design-system addition for product sticky headers. Do not treat it as a new visual variant.
• 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.