fix(web-ui): allow Tab focus traversal inside modal dialogs

[bobleer]

Summary

• Keep the global IDE-style Tab blocker for app chrome, but allow Tab / Shift+Tab inside modal dialogs ([role="dialog"] / [aria-modal="true"]).
• Fixes Tab not moving between inputs in Remote SSH “New Connection” and Account Login forms (and other Modal-based forms).

Fixes #

Type and Areas

Type:

bug fix / UI/UX

Areas:

web UI

Motivation / Impact

Global Tab preventDefault in main.tsx blocked focus traversal everywhere except Monaco and xterm. Modal forms (SSH connect, account login) could not Tab between fields. Users can now Tab inside dialogs; main chrome Tab behavior is unchanged.

Verification

• pnpm run type-check:web (pass)
• Manual: open Remote SSH → New Connection and Account Login; Tab / Shift+Tab should move between inputs and stay trapped in the modal

Reviewer Notes

Root cause is the capture-phase Tab blocker added in 5566db603 (PR #150). This change only widens the allowlist; it does not remove the global blocker.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.