Better timestamps (add date)

[Klar]

The web UI parses Go's slog log lines and renders just the time portion.

We could change this line in src/web/frontend/src/lib/utils.js:37:

// Current — shows only HH:MM:SS
time = new Date(kv.time).toLocaleTimeString([], { hour: '2-digit', minute: '2-digit', second: '2-digit', hour12: false })

// Change to — shows YYYY-MM-DD HH:MM:SS
time = new Date(kv.time).toLocaleString([], { year: 'numeric', month: '2-digit', day: '2-digit', hour: '2-digit', minute: '2-digit', second: '2-digit', hour12: false })