refactor(web): extract shared UI and host packages - #842

Why?

The Stovepipe UI needs the same navigation, refresh controls, URL handling, styling, and host integration that SubmitQueue already has. Extract those pieces first so the next PR can add Stovepipe without copying SubmitQueue code, and reviewers can assess the refactoring separately.

What?

• Move shared React navigation, polling, path-segment helpers, and styles into web/platform (@submitqueue/web-platform).
• Move common Basic auth, Node gRPC transport, Next.js navigation, and readiness checks into web/service/shared (@submitqueue/web-service-shared). Service-specific configuration stays in the host.
• Update SubmitQueue to import the shared implementations directly, preserving its public exports and existing behavior.
• Share the Bazel library build, packaging, and lint setup, and update workspace and package-consumer checks.

Test Plan

Shared-package checks and the existing SubmitQueue browser suite passed; the latest rebased stack passed all 31 targets with ./tool/bazel test //web:check //web/test/e2e/stovepipe:web_test --test_output=errors. To validate this PR independently:

./tool/bazel test //web:check //web/test/e2e:web_test --test_output=errors

Repository formatting, lint, module tidy, and Gazelle checks also passed.

Revert Plan

Revert dependent PRs #844, #838, and #837 first if merged, then revert this PR to restore the original SubmitQueue package layout.

Stack

1. refactor(web): extract shared UI and host packages #842 — shared-package refactoring (this PR; based on main).
2. [DRAFT/WIP] feat(web): add Stovepipe request status UI #837 — Stovepipe frontend (based on refactor(web): extract shared UI and host packages #842).
3. [DRAFT/WIP] test(web): add Stovepipe coverage and align E2E suites #838 — browser coverage and E2E organization (based on [DRAFT/WIP] feat(web): add Stovepipe request status UI #837).
4. Draft: refactor(web): let hosts handle request logging #844 — host logging integration (based on [DRAFT/WIP] test(web): add Stovepipe coverage and align E2E suites #838).

Issue Links

None — no issue was supplied for this work.