refactor(web): extract shared UI and host packages

[mnoah1]

Why?

Much of the structure around the new SubmitQueue UI is reusable for a Stovepipe UI as well. This PR pulls out common components into shared packages that can be used across both services to minimize duplication.

What?

• Move shared React navigation, polling, timestamp formatting, 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 32 targets with ./tool/bazel test //web:check //web/test/e2e/submitqueue:web_test //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
2. feat(web): add Stovepipe request status UI #837 — Stovepipe frontend
3. test(web): add Stovepipe coverage and align E2E suites #838 — browser coverage and E2E organization
4. refactor(web): let hosts handle request logging #844 — host logging integration