task(B1): unique row/block ids for seating (fixes BUG-1)

frontend/src/services/seatingService.ts

@@ -159,6 +159,13 @@ export const SEATING_TEMPLATES: SeatingTemplate[] = [
   },
 ];
 
+let seqCounter = 0;
+/** Eindeutige, kollisionsfreie ID mit Präfix (Zeit + Sequenz + Zufall). */
+function nextUid(prefix: string): string {
+  seqCounter += 1;
+  return `${prefix}_${Date.now().toString(36)}_${seqCounter.toString(36)}_${Math.random().toString(36).slice(2, 8)}`;
+}
+
 export class SeatingService {
   private generateId(): string {
     return `el_${Date.now()}_${Math.random().toString(36).slice(2, 9)}`;
@@ -189,6 +196,7 @@ export class SeatingService {
   createSeatingRow(x: number, y: number, layerId: string, config: Partial<SeatingRowConfig> = {}): CADElement[] {
     const cfg = { ...DEFAULT_ROW, ...config };
     const elements: CADElement[] = [];
+    const rowId = nextUid('row');
     const totalWidth = (cfg.count - 1) * cfg.spacing + cfg.chairWidth;
     const startX = x - totalWidth / 2 + cfg.chairWidth / 2;
 
@@ -217,7 +225,7 @@ export class SeatingService {
           outlineColor: '#2a5a99',
           seatType: 'standard',
           rowIndex: i,
-          rowId: `row_${Date.now()}`,
+          rowId,
         },
       });
     }
@@ -233,9 +241,10 @@ export class SeatingService {
     const startX = x - totalW / 2 + cfg.chairWidth / 2;
     const startY = y - totalH / 2 + cfg.chairHeight / 2;
     const rot = cfg.rotation * Math.PI / 180;
-    const blockId = `block_${Date.now()}`;
+    const blockId = nextUid('block');
 
     for (let row = 0; row < cfg.rows; row++) {
+      const rowId = nextUid('row');
       const offset = cfg.rowOffset * (row % 2);
       for (let col = 0; col < cfg.cols; col++) {
         const lx = startX + col * cfg.colSpacing + offset;
@@ -263,6 +272,7 @@ export class SeatingService {
             rowIndex: row,
             colIndex: col,
             blockId,
+            rowId,
           },
         });
       }