feat: Extend JoinNode to support 8 input paths

- Increased from 3 to 8 input handles (path_1 through path_8)
- Evenly distributed across top edge (11%, 22%, 33%, ..., 89%)
- Backend already supports unlimited inputs dynamically
- Unused handles are ignored (no edges = no check)

Join strategies for missing inputs:
- wait_all: Fails if any connected path fails
- wait_any: Succeeds if at least 1 path succeeds
- best_effort: Always succeeds

User can still chain multiple Joins if >8 inputs needed.
Part 3: Inline Prompts - workflow flexibility

frontend/src/components/workflow/nodes/JoinNode.jsx

@@ -42,24 +42,54 @@ export function JoinNode({ data, selected }) {
         </div>
       </div>
 
-      {/* Mehrere Target Handles für eingehende Pfade */}
+      {/* Mehrere Target Handles für eingehende Pfade (bis zu 8) */}
       <Handle
         type="target"
         position={Position.Top}
         id="path_1"
-        style={{ left: '25%', background: '#17A2B8' }}
+        style={{ left: '11%', background: '#17A2B8' }}
       />
       <Handle
         type="target"
         position={Position.Top}
         id="path_2"
-        style={{ left: '50%', background: '#17A2B8' }}
+        style={{ left: '22%', background: '#17A2B8' }}
       />
       <Handle
         type="target"
         position={Position.Top}
         id="path_3"
-        style={{ left: '75%', background: '#17A2B8' }}
+        style={{ left: '33%', background: '#17A2B8' }}
+      />
+      <Handle
+        type="target"
+        position={Position.Top}
+        id="path_4"
+        style={{ left: '44%', background: '#17A2B8' }}
+      />
+      <Handle
+        type="target"
+        position={Position.Top}
+        id="path_5"
+        style={{ left: '56%', background: '#17A2B8' }}
+      />
+      <Handle
+        type="target"
+        position={Position.Top}
+        id="path_6"
+        style={{ left: '67%', background: '#17A2B8' }}
+      />
+      <Handle
+        type="target"
+        position={Position.Top}
+        id="path_7"
+        style={{ left: '78%', background: '#17A2B8' }}
+      />
+      <Handle
+        type="target"
+        position={Position.Top}
+        id="path_8"
+        style={{ left: '89%', background: '#17A2B8' }}
       />
 
       {/* Ein Source Handle für konsolidierten Ausgang */}