feat(web): canonical keyboard traversal and focus rings

[Pavel Feldman (pavelfeldman)]

Summary

• Make TabbedPane tabs real <button>s so every header is a native Tab stop and Space/Enter selects — this also gives the snapshot Action/Before/After tablist the keyboard navigation it was missing.
• Stop CodeMirror from capturing Tab/Shift-Tab, so focus is no longer trapped inside source/network/locator/aria editors.
• Add keyboard-only :focus-visible rings to tabs, toolbar buttons, text/search inputs, toolbar selects, and CodeMirror editors.

Fixes#41422

[github-actions]

Test results for "MCP"

1 failed
❌ [firefox] › mcp/http.spec.ts:349 › client should receive list roots request @mcp-windows-latest-firefox

7379 passed, 1122 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

2 failed
❌ [chromium-library] › library/browsercontext-add-init-script.spec.ts:28 › should work without navigation, after all bindings @chromium-ubuntu-22.04-arm-node20
❌ [chromium-library] › library/browsercontext-expose-function.spec.ts:77 › should be callable from-inside addInitScript @chromium-ubuntu-22.04-arm-node20

3 flaky

⚠️ [chromium-library] › library/har-websocket.spec.ts:235 › should attach websocket messages `@frozen-time-library-chromium-linux`
⚠️ [chromium-library] › library/chromium/chromium.spec.ts:211 › should intercept service worker requests (main and within) `@chromium-ubuntu-22.04-node22`
⚠️ [chromium-library] › library/video.spec.ts:645 › screencast › should capture full viewport `@chromium-ubuntu-22.04-node22`

49007 passed, 1142 skipped

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Merge workflow run.

[Aditya Kumar Gupta (triemerge)]

Nice approach, i think the html-reporter might have the same gap with its own TabbedPane still on <div role="tab">. wondering if it'd be worth a follow-up there too.