refactor(ui): remove dead rail unarchive

[Phoenix500526]

Summary

Remove the unreachable task-rail Unarchive path. Archived sessions are
excluded before rail projection, so SessionRowActions.onUnarchive and its
rendering branch could not run in production.

Keep the active restore paths unchanged: Settings > Archived Tasks, the
session controller and IPC boundary, archived projects, and Work Board.

Fixes #5189

Verification

• npm exec biome lint -- <9 changed files> — passed
• npm run format:check — passed (2,075 files)
• npm --workspace @maka/ui run build — passed
• npm --workspace @maka/ui run test:dist — passed (430 tests)
• npm --workspace @maka/desktop run typecheck — passed
• Storybook smoke was not run; this removes an unreachable rail branch and
  does not change a rendered reachable state.

AI use

Select exactly one:

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

Tool(s) and scope: OpenAI Codex analyzed reachability, implemented the cleanup,
updated fixtures, ran verification, and drafted this pull request.

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