Added support for Streamdeck Pedal and updated UI to better fit the Packed UI style

pirp/tools/migrate_storno_mahnung.sql

@@ -0,0 +1,20 @@
+-- Migration: Storno-Rechnungen + Mahnungen
+-- Anwendung: psql -U pirp_user -d pirp -f tools/migrate_storno_mahnung.sql
+
+-- Storno: zwei neue Spalten in invoices
+ALTER TABLE invoices
+    ADD COLUMN IF NOT EXISTS storno_of INTEGER REFERENCES invoices(id) ON DELETE SET NULL,
+    ADD COLUMN IF NOT EXISTS is_storno BOOLEAN NOT NULL DEFAULT FALSE;
+
+-- Mahnungen: neue Tabelle
+CREATE TABLE IF NOT EXISTS mahnungen (
+    id SERIAL PRIMARY KEY,
+    invoice_id INTEGER NOT NULL REFERENCES invoices(id) ON DELETE CASCADE,
+    mahnung_date DATE NOT NULL,
+    level INTEGER NOT NULL DEFAULT 1 CHECK (level IN (1,2,3)),
+    fee_amount NUMERIC(12,2) NOT NULL DEFAULT 0,
+    pdf_path TEXT,
+    created_at TIMESTAMPTZ DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS idx_mahnungen_invoice_id ON mahnungen(invoice_id);