fix(dash): refresh stats on an interval and compact feed timestamps

[fu351]

Slice

• Repo: doberman-core
• Feature / Slice: dash polish follow-up (found while recording the README hero GIF)

What this PR does

The stats row was fetched once at page load and froze at those values while the live feed kept filling - visibly wrong on camera (feed shows 7 decisions, counters read 0). Stats now refresh every 5s via the same authed GET. Feed timestamps render as compact HH:MM:SS sliced from the ISO string (full precision stays in doberman log / the TUI).

Tests added (run in CI)

• tests/unit/test_dash_polish.py: stats-refresh interval present; compact timestamp form present and the old full-ISO render gone. Full dash suite: 58 passed.

Public-release safety (doberman-core only)

• Contains nothing from the not-allowed list
• Core still builds/tests/runs with NO enterprise package installed

Security checklist

• Fails closed on error / uncertainty (stats fetch failure renders 'stats unavailable', nothing else changes)
• No secret, full file, or unredacted prompt logged or committed
• Any guardrail/learning change is raise-only (N/A - UI only)
• Every BLOCK/AUTH carries reason codes + a human explanation (N/A)
• doberman-core does not import doberman_enterprise

Edge cases covered / Deviations from plan / Risks introduced

• textContent-only rendering discipline unchanged (asserted by existing test); no new endpoints; missing/short ts renders '-'.