Enhance ShellV2 UI with status indicators and layout updates

[KCarretto]

Enhanced the ShellV2 page in tavern/internal/www with requested UI features:

1. Breadcrumbs: Added navigation breadcrumb.
2. Badge: Added "Pre-alpha release" badge.
3. Portal Status: Added indicator showing active portal ID or "non-interactive" status with tooltip explaining portal functionality. Listens for PORTAL_UPGRADE WebSocket signal.
4. Callback Timer: Added countdown to next beacon check-in, highlighting missed check-ins in red.
5. Layout: Updated to flex column layout with header and footer.

Verified changes by running npm run build and npm run test (which passed). Included rebuilt assets in tavern/internal/www/build.

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PR created automatically by Jules for task 14908132475075555183 started by @KCarretto

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[github-actions]

Summary

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
2643    ±0	2643    ±0	0    ±0	0    ±0	0    ±0	0    ±0	1ms    ±0

Previous Results

Build 🏗️	Result 🧪	Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
#1096	✅	2643	2643	0	0	0	0	36.8s

Insights

Average Tests per Run	Total Flaky Tests	Total Failed	Slowest Test (p95)
2643	0	0	6.0s

Slowest Tests

Test 📝	Results 📊	Duration (avg) ⏱️	Duration (p95) ⏱️
TestDockerExecutor_Build_ContextCancellation	1	6.0s	6.0s
eldritch-libsys: std::dll_inject_impl::tests::test_dll_inject_simple	1	5.2s	5.2s
TestInteractiveShell	1	5.0s	5.0s
TestOtherStreamOutput	1	5.0s	5.0s
TestDockerExecutor_Build_SimpleEcho	1	4.3s	4.3s
imix::bin/imix: install::tests::test_install_execution	3	1.5s	4.3s
imix::bin/imix: install::tests::test_install_execution	3	1.5s	4.3s
imix::bin/imix: install::tests::test_install_execution	3	1.5s	4.3s
imix::bin/imix: tests::task_tests::test_task_streaming_output	3	3.0s	3.0s
imix::bin/imix: tests::task_tests::test_task_streaming_output	3	3.0s	3.0s

_{🎉 No failed tests in this run. | 🍂 No flaky tests in this run.}

Github Test Reporter by CTRF 💚

🔄 This comment has been updated