Dashboard post-merge fixes: counter, ex-div day, dividend mini

[fleveque]

Three bugs reported in prod after #173 merged.

1. Quick-stat counters stuck at 0

AnimatedCounter (in DashboardGreeting) rendered 0 holdings / 0 on radar even when the user had data.

Root cause. useCountUp only animated on the first viewport intersect. Sequence on a real account:

1. Mount → useHoldings() loading → holdings.length === 0 → target = 0.
2. IntersectionObserver fires → startedRef.current = true → animate 0 → 0.
3. Data arrives → holdings.length === N → effect re-runs with new target.
4. Re-run sees startedRef.current === true → skips → counter sticks at 0.

Fix. Rewrote useCountUp so it animates from the previous value to the new target on every change, with visibility tracked separately (once) but not gating subsequent updates. Reduced-motion still short-circuits.

2. "SBUX in 5d" greeting vs "in 4d" in upcoming list

DashboardGreeting and UpcomingExDividends disagreed by 1 day for the same stock.

Root cause. Greeting used Math.ceil, UpcomingExDividends uses Math.round. Server ships date-only strings (parsed as UTC midnight); compared against local midnight, that's a fractional diff (e.g. 4.08 days). ceil → 5, round → 4.

Fix. One-line change in Greeting to use Math.round.

3. DividendIncomeMini hidden despite recorded dividends

User had several dividends, mini didn't render.

Root cause. /dividends/chart_data returns 24 buckets per currency: 12 past + 12 future. Past months carry actual (paid), future ones carry projected. My slice(-12) grabbed the last 12 (= current month + 11 future), where actual is mostly null — so the "sum of actual values" sat at 0 unless the current month had a payment, and the card hid itself.

Fix. Filter to past-only entries (actual !== null) and take the last 12 of those. Robust to wider server windows (range=full).

Test plan

• npx tsc --noEmit — clean
• Manual: logged in with a populated account → holdings/radar counters animate up to real values, next ex-div day matches the list below
• Manual: account with historical dividends → DividendIncomeMini renders with this-month total + 12-bar sparkline
• Manual: empty account → counters animate to 0, mini stays hidden
• Reduced motion: counts jump to final immediately

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