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Each summary card (Einnahmen, Ausgaben, Saldo) now shows a trend line comparing the current month to the previous one. The previous month's summary is fetched in parallel via the existing /budget/summary endpoint, so there is no extra round-trip latency. Positive deltas render in green (▲), negative in red (▼), unchanged in neutral grey (—). Closes BL-02. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>