feat: implement rewireConnection operation (Phase 1, Task 1)

Added intuitive rewireConnection operation for changing connection targets
in a single semantic step: "rewire from X to Y"

Changes:
- Added RewireConnectionOperation type with from/to semantics
- Implemented validation (checks source, from, to nodes and connection existence)
- Implemented operation as remove + add wrapper
- Added 8 comprehensive tests covering all scenarios
- All 134 tests passing (126 Phase 0 + 8 new)

Test Coverage:
- Basic rewiring
- Rewiring with sourceOutput specified
- Preserving parallel connections
- Error handling (source/from/to not found, connection doesn't exist)
- IF node branch rewiring

Expected Impact: 4/10 → 9/10 rating for rewiring tasks

Related: Issue #272 Phase 1 implementation
Phase 0 PR: #274

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/types/workflow-diff.ts

@@ -87,6 +87,16 @@ export interface UpdateConnectionOperation extends DiffOperation {
   };
 }
 
+export interface RewireConnectionOperation extends DiffOperation {
+  type: 'rewireConnection';
+  source: string;      // Source node name or ID
+  from: string;        // Current target to rewire FROM
+  to: string;          // New target to rewire TO
+  sourceOutput?: string;  // Optional: which output to rewire (default: 'main')
+  targetInput?: string;   // Optional: which input type (default: 'main')
+  sourceIndex?: number;   // Optional: which source index (default: 0)
+}
+
 // Workflow Metadata Operations
 export interface UpdateSettingsOperation extends DiffOperation {
   type: 'updateSettings';
@@ -140,6 +150,7 @@ export type WorkflowDiffOperation =
   | AddConnectionOperation
   | RemoveConnectionOperation
   | UpdateConnectionOperation
+  | RewireConnectionOperation
   | UpdateSettingsOperation
   | UpdateNameOperation
   | AddTagOperation
@@ -187,8 +198,8 @@ export function isNodeOperation(op: WorkflowDiffOperation): op is
 }
 
 export function isConnectionOperation(op: WorkflowDiffOperation): op is
-  AddConnectionOperation | RemoveConnectionOperation | UpdateConnectionOperation | CleanStaleConnectionsOperation | ReplaceConnectionsOperation {
-  return ['addConnection', 'removeConnection', 'updateConnection', 'cleanStaleConnections', 'replaceConnections'].includes(op.type);
+  AddConnectionOperation | RemoveConnectionOperation | UpdateConnectionOperation | RewireConnectionOperation | CleanStaleConnectionsOperation | ReplaceConnectionsOperation {
+  return ['addConnection', 'removeConnection', 'updateConnection', 'rewireConnection', 'cleanStaleConnections', 'replaceConnections'].includes(op.type);
 }
 
 export function isMetadataOperation(op: WorkflowDiffOperation): op is