01a042cc - Keep portfolio chart visible when holdings are zero

[TaprootFreakAI]

EN:
The portfolio development chart disappeared for time windows where every holding is zero.
The cubit now keeps a Y-range from 0 so the line stays drawn, and holds the last value before the window so the stroke spans the selected period.
A dashboard golden records the all-zero MAX view; the customer-report 1W–1J goldens show that full-width zero line on a 0…10 axis.
Unit tests cover an all-zero series, a one-week window of zeros, and carrying a pre-window sample to minX.

DE:
Die Bestandsentwicklung verschwand in Zeitfenstern, in denen jeder Punkt 0 ist.
Der Cubit hält jetzt eine Y-Spanne ab 0, damit die Linie gezeichnet bleibt, und übernimmt den letzten Wert vor dem Fenster, damit der Strich die gewählte Periode ausfüllt.
Ein Dashboard-Golden dokumentiert die Null-MAX-Ansicht; die Kunden-Goldens 1W–1J zeigen diese volle Null-Linie auf einer Achse 0…10.
Unit-Tests decken eine Null-Serie, ein 1W-Null-Fenster und das Nachziehen eines Werts vor minX ab.

Details

When every visible point is 0, average * 0.05 was 0, so minY == maxY == 0 and LineChart drew no curve. The cubit now falls back to a 5.0 currency-unit floor so the chart has a Y-range. Holdings cannot go negative: the bottom line is always clamped to 0 (scale 0…10 for an all-zero series), not centered through negative labels.

A clipped period (1W/1M/3M/1J) previously started the stroke at the first interior sample. If that sample sat months into the window, the line began mid-chart. The last sample before minX is now held at the window edge so the stroke spans the selected period. An empty window (every sample older than the period) stays empty.

dashboard_portfolio_chart_zero.png is the all-zero MAX view. After #953, the mixed-history 1W/1M/3M/1J goldens pin the full-width zero line on the 0-axis.

[TaprootFreakAI]

EN:
Ready after 2 review passes.
The portfolio chart stays visible when every holding in the selected window is zero.

DE:
Bereit nach 2 Review-Durchläufen.
Die Bestandskurve bleibt sichtbar, wenn im gewählten Fenster jeder Bestand 0 ist.

Details

Review pass 1 (98eed05): 0 findings on quality and logic. Coverage Floor Gate failed at 99.9% vs a 100% line floor because the old deviation <= 0 collapse path was no longer reached.

Review pass 2 (e1aee89): that dead branch was removed; 0 findings on quality and logic.

Open comments: none (issue comments, reviews, inline comments, and review threads all empty).

Mergeability: mergeable=MERGEABLE at head e1aee89. mergeStateStatus=BLOCKED is the human-approval requirement, not a conflict.

CI at e1aee89: Analyze & Test success, Visual Regression success, Coverage Floor Gate success, BitBox quirks audit success. Maestro handbook flows skipped (opt-in label not set; not a required check).

[TaprootFreakAI]

EN:
The all-zero portfolio chart baseline is now in the PR.

DE:
Die Baseline für den Chart ohne Bestand ist jetzt im PR.