refactor(desktop): extract Workbar as a feature slice

[chihumyum]

Summary

• Extract Workbar layout, tools, and dynamic-resource lifecycles into a feature-owned vertical slice.
• Keep Electron bridge access in a Desktop adapter; the Workbar feature no longer imports AppShell, preload, or main, and does not access window.maka.
• Reduce AppShell to Workbar host inputs plus the host / commands / selectors surface while preserving storage, IPC, layout, mounting, and cleanup behavior.

Refs #3439

Verification

• npm run lint — passed (2,513 files)
• npm run format:check — passed (1,565 files)
• npm run build — passed
• npm run typecheck — passed
• npm --workspace @maka/desktop test — passed (1,061 tests, 124 suites)
• npx knip --workspace apps/desktop — passed
• npx knip --workspace packages/ui — passed
• npm run astryx:surface-inventory — passed (199 files, 1 exclusion)
• npm --workspace @maka/desktop run build-storybook — passed
• npm --workspace @maka/desktop run smoke:storybook — passed (162 stories)
• npm --workspace @maka/desktop run e2e — passed (41 passed, 1 skipped)

Review focus

• v1/v2 to v3 Workbar storage hydration and transient-field filtering
• Terminal ownership, stale-start fencing, close/session-switch cleanup, and RAF disposal
• Side Chat collapse/close/source-switch behavior and late fork/send disposal fencing
• Desktop service mapping and subscription disposal, especially Inspector pagination and Session usage authority
• CSS relocation/import order and right/bottom/narrow Workbar visual parity

AI use

Select exactly one:

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Codex — architecture analysis, implementation, tests, latest-main replay, lifecycle race review, and pull request preparation. The human contributor reviewed the contribution and accepts responsibility for it.

All substantive commits include Generated-by: Codex; retain the trailer in the final squash commit.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No