feat: 15 UPC proceeding types in 3 groups + category field

Added 10 new UPC types: DNI, EPO, AMD, CCI, EVP, DAM, COS, REH, DEF, RST.
Grouped as: Hauptverfahren / Verfahren im Verfahren / Rechtsbehelfe.
Frontend dropdown shows sub-groups within jurisdiction. German names throughout.

backend/internal/models/deadline_rule.go

@@ -39,6 +39,7 @@ type ProceedingType struct {
 	Name         string  `db:"name" json:"name"`
 	Description  *string `db:"description" json:"description,omitempty"`
 	Jurisdiction *string `db:"jurisdiction" json:"jurisdiction,omitempty"`
+	Category     *string `db:"category" json:"category,omitempty"`
 	DefaultColor string  `db:"default_color" json:"default_color"`
 	SortOrder    int     `db:"sort_order" json:"sort_order"`
 	IsActive     bool    `db:"is_active" json:"is_active"`