feat: implement smart parameters (branch, case) for multi-output nodes (Phase 1, Task 2)

Add intuitive semantic parameters for working with IF and Switch nodes:
- branch='true'|'false' for IF nodes (maps to sourceOutput)
- case=N for Switch nodes (maps to sourceIndex)
- Smart parameters resolve to technical parameters automatically
- Explicit parameters always override smart parameters

Implementation:
- Added branch and case parameters to AddConnectionOperation and RewireConnectionOperation interfaces
- Created resolveSmartParameters() helper method to map semantic to technical parameters
- Updated applyAddConnection() to use smart parameter resolution
- Updated applyRewireConnection() to use smart parameter resolution
- Updated validateRewireConnection() to validate with resolved smart parameters

Tests:
- Added 8 comprehensive tests for smart parameters feature
- All 141 workflow diff engine tests passing
- Coverage: 91.7% overall

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

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

src/types/workflow-diff.ts

@@ -64,6 +64,9 @@ export interface AddConnectionOperation extends DiffOperation {
   targetInput?: string; // Default: 'main'
   sourceIndex?: number; // Default: 0
   targetIndex?: number; // Default: 0
+  // Smart parameters for multi-output nodes (Phase 1 UX improvement)
+  branch?: 'true' | 'false'; // For IF nodes: maps to sourceOutput
+  case?: number; // For Switch nodes: maps to sourceIndex
 }
 
 export interface RemoveConnectionOperation extends DiffOperation {
@@ -95,6 +98,9 @@ export interface RewireConnectionOperation extends DiffOperation {
   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)
+  // Smart parameters for multi-output nodes (Phase 1 UX improvement)
+  branch?: 'true' | 'false'; // For IF nodes: maps to sourceOutput
+  case?: number; // For Switch nodes: maps to sourceIndex
 }
 
 // Workflow Metadata Operations