[MT-23018] Add accessible Tech Info tooltips

[kyrylo-yevdokymov]

What & why

Implements MT-23018, a sub-task of MT-22849.

Adds explanatory SMTP Transaction Info and Email Headers tooltips. The component keeps tooltip controls outside semantic headings, exposes descriptions through aria-describedby, remains open while hovered, and consumes Escape without triggering message-level navigation.

Impact

Technical email metadata is easier to understand and the help content is usable by pointer and keyboard users.

Verification

• npm test — 62 tests passed
• npm run lint — 0 errors; 4 existing warnings
• npm run build — passed
• git diff --check main...codex/mt-23018-tech-info-tooltips — passed

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[kyrylo-yevdokymov]

Replaced by #36 using the repository-standard fix/mt-23018-tech-info-tooltips branch.