feat: use 24-hour time and ISO date-time formats in the web UI

[sg]

Summary

Standardizes timestamp display across the web UI to two formats: 24-hour clock time for compact list views, and ISO-style date-time for detail/inspector views (no AM/PM, no raw epochs).

New shared web-ui/src/time.js:

• fmtTime(ts) → HH:MM:SS (24-hour)
• fmtDateTime(ts) → YYYY-MM-DD HH:MM:SS (ISO-style local)

Changes

• Messages screen — message rows use 24-hour fmtTime (was AM/PM).
• Packets list — row time uses 24-hour fmtTime (was AM/PM).
• Packets inspector — the decoded payload's timestamp renders ISO via FieldBreakout (was raw epoch); matches timestamp / *_timestamp / *_at keys.
• Manage → Audit log — the ts epoch column renders ISO via a new cellAt() in the generic table.
• Removed the duplicated AM/PM fmtTime from Messages and Packets; a grep confirms no toLocaleTimeString remains. Contacts timestamps were already 24-hour/ISO-ish and are left unchanged.

Testing

Front-end only (no API/schema changes). npm run build is clean; formatter outputs sanity-checked (05:03:57, 2026-06-13 05:03:57). Rebuilt webapi/static/ assets included.