feat(ui): migrate desktop and web to v4 shared workbench

[DeliciousBuding]

Summary

• Migrates Desktop 5173 and Web 5174 to the current shared v4 workbench baseline; agenthub-design/desktop remains historical visual reference only.
• Adds/extends shared workbench shell, transcript blocks, composer, inspector, floating controls, pages, design icons, demo runtime, shared i18n and theme sync.
• Keeps Desktop-specific capability in app/desktop/src/platform and Tauri host boundaries, and enforces Web 5174 as Hub-only with no Tauri/Local Edge boundary leak.
• Documents the frozen frontend state, design parity evidence, merge readiness, and the next Desktop Edge / Web Hub production integration plan.

Validation

• git diff --check
• .\scripts\verify-v4-old-ui-active-paths.ps1 (44/44)
• .\scripts\verify-web-hub-boundary.ps1 (15/15)
• cd app\shared; corepack.cmd pnpm exec vitest run src\workbench\AgentHubWorkbench.test.tsx src\workbench\designIcons.test.tsx --reporter=dot (2 files / 31 tests)
• cd app\desktop; corepack.cmd pnpm exec vitest run src\platform\desktopPlatform.test.ts --reporter=dot (1 file / 1 test)
• cd app\desktop; corepack.cmd pnpm typecheck
• cd app\desktop; corepack.cmd pnpm build (passes with existing chunk/circular chunk warnings)
• cd app\web; corepack.cmd pnpm exec vitest run src\api\hubAuth.test.ts src\platform\webPlatform.test.ts --reporter=dot (2 files / 14 tests)
• cd app\web; corepack.cmd pnpm typecheck
• cd app\web; corepack.cmd pnpm build (passes with existing chunk warning)

Known Follow-ups

• Branch is draft-only until refreshed against latest dev/delicious233 (11 behind / 35 ahead at creation time).
• Desktop/Tauri Host API split remains open and is tracked in docs/desktop-edge-web-integration-plan.md.
• Desktop Local Edge runtime facade still needs production hardening; Web Hub-only boundary is guarded, but broader Web Hub runtime E2E remains follow-up.
• Backend and mobile changes currently present in the local worktree were not included in this UI PR and need owner-specific handling.
• docs/review-2026-06-07-glm-5.1/ remains local reference material unless explicitly accepted into the PR.

Notes

• This PR is the Desktop/Web v4 shared UI clean rebuild and merge-readiness package.
• It does not claim Edge backend production hardening, Desktop Tauri host split, or full production CRUD/mutation coverage is complete.

[DeliciousBuding]

Merge-readiness note (2026-06-08): I attempted to refresh this branch against origin/dev/delicious233 in a clean temporary worktree. The only textual merge conflict was app/shared/package.json; the intended resolution is to keep dev's React >=19.2.7 constraints and keep the v4 shared exports/icon dependencies. After resolving that and refreshing pnpm-lock, shared focused tests, Web focused tests, Web typecheck/build, verify-v4-old-ui-active-paths, and verify-web-hub-boundary still passed. Desktop typecheck/build then failed because dev/delicious233 now has app/desktop exactOptionalPropertyTypes=true, exposing pre-existing Desktop optional-property debt across app/desktop/src (edgeClient, TeamRunConsole, workspaceStore, useTopMenuConfig, etc.). I did not push a merge commit because that Desktop strict-typing cleanup is larger than a mechanical conflict resolution and should be handled as a focused follow-up before marking this PR ready. The local temporary merge worktree has been removed.