fix: add string normalization for special characters in node names

Fixes #270

## Problem
Connection operations (addConnection, removeConnection, etc.) failed when node
names contained special characters like apostrophes, quotes, or backslashes.

Default n8n Manual Trigger node: "When clicking 'Execute workflow'" caused:
- Error: "Source node not found: \"When clicking 'Execute workflow'\""
- Node shown in available nodes list but string matching failed
- Users had to use node IDs as workaround

## Root Cause
The `findNode()` method in WorkflowDiffEngine performed exact string matching
without normalization. When node names contained special characters, escaping
differences between input strings and stored node names caused match failures.

## Solution
### 1. String Normalization (Primary Fix)
Added `normalizeNodeName()` helper method:
- Unescapes single quotes: \' → '
- Unescapes double quotes: \" → "
- Unescapes backslashes: \\ → \
- Normalizes whitespace

Updated `findNode()` to normalize both search string and node names before
comparison, while preserving exact UUID matching for node IDs.

### 2. Improved Error Messages
Enhanced validation error messages to show:
- Node IDs (first 8 characters) for quick reference
- Available nodes with both names and ID prefixes
- Helpful tip about using node IDs for special characters

### 3. Comprehensive Tests
Added 6 new test cases covering:
- Apostrophes (default Manual Trigger scenario)
- Double quotes
- Backslashes
- Mixed special characters
- removeConnection with special chars
- updateNode with special chars

All tests passing: 116/116 in workflow-diff-engine.test.ts

### 4. Documentation
Updated tool documentation to note:
- Special character support since v2.15.6
- Node IDs preferred for best compatibility

## Affected Operations
All 8 operations using findNode() now support special characters:
- addConnection, removeConnection, updateConnection
- removeNode, updateNode, moveNode
- enableNode, disableNode

## Testing
Validated with n8n-mcp-tester agent:
✅ addConnection with apostrophes works
✅ Default Manual Trigger name works
✅ Improved error messages show IDs
✅ Double quotes handled correctly
✅ Node IDs work as alternative

## Impact
- Fixes common user pain point with default n8n node names
- Backward compatible (only makes matching MORE permissive)
- Minimal performance impact (normalization only during validation)
- Centralized fix (one method fixes all 8 operations)

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

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

src/services/workflow-diff-engine.ts

@@ -384,12 +384,16 @@ export class WorkflowDiffEngine {
     const targetNode = this.findNode(workflow, operation.target, operation.target);
 
     if (!sourceNode) {
-      const availableNodes = workflow.nodes.map(n => n.name).join(', ');
-      return `Source node not found: "${operation.source}". Available nodes: ${availableNodes}`;
+      const availableNodes = workflow.nodes
+        .map(n => `"${n.name}" (id: ${n.id.substring(0, 8)}...)`)
+        .join(', ');
+      return `Source node not found: "${operation.source}". Available nodes: ${availableNodes}. Tip: Use node ID for names with special characters (apostrophes, quotes).`;
     }
     if (!targetNode) {
-      const availableNodes = workflow.nodes.map(n => n.name).join(', ');
-      return `Target node not found: "${operation.target}". Available nodes: ${availableNodes}`;
+      const availableNodes = workflow.nodes
+        .map(n => `"${n.name}" (id: ${n.id.substring(0, 8)}...)`)
+        .join(', ');
+      return `Target node not found: "${operation.target}". Available nodes: ${availableNodes}. Tip: Use node ID for names with special characters (apostrophes, quotes).`;
     }
 
     // Check if connection already exists
@@ -417,10 +421,16 @@ export class WorkflowDiffEngine {
     const targetNode = this.findNode(workflow, operation.target, operation.target);
 
     if (!sourceNode) {
-      return `Source node not found: ${operation.source}`;
+      const availableNodes = workflow.nodes
+        .map(n => `"${n.name}" (id: ${n.id.substring(0, 8)}...)`)
+        .join(', ');
+      return `Source node not found: "${operation.source}". Available nodes: ${availableNodes}. Tip: Use node ID for names with special characters.`;
     }
     if (!targetNode) {
-      return `Target node not found: ${operation.target}`;
+      const availableNodes = workflow.nodes
+        .map(n => `"${n.name}" (id: ${n.id.substring(0, 8)}...)`)
+        .join(', ');
+      return `Target node not found: "${operation.target}". Available nodes: ${availableNodes}. Tip: Use node ID for names with special characters.`;
     }
 
     const sourceOutput = operation.sourceOutput || 'main';
@@ -791,23 +801,58 @@ export class WorkflowDiffEngine {
   }
 
   // Helper methods
+
+  /**
+   * Normalize node names to handle special characters and escaping differences.
+   * Fixes issue #270: apostrophes and other special characters in node names.
+   *
+   * @param name - The node name to normalize
+   * @returns Normalized node name for comparison
+   */
+  private normalizeNodeName(name: string): string {
+    return name
+      .trim()                    // Remove leading/trailing whitespace
+      .replace(/\\'/g, "'")      // Unescape single quotes: \' -> '
+      .replace(/\\"/g, '"')      // Unescape double quotes: \" -> "
+      .replace(/\\\\/g, '\\')    // Unescape backslashes: \\ -> \
+      .replace(/\s+/g, ' ');     // Normalize multiple spaces to single space
+  }
+
+  /**
+   * Find a node by ID or name in the workflow.
+   * Uses string normalization to handle special characters (Issue #270).
+   *
+   * @param workflow - The workflow to search in
+   * @param nodeId - Optional node ID to search for
+   * @param nodeName - Optional node name to search for
+   * @returns The found node or null
+   */
   private findNode(workflow: Workflow, nodeId?: string, nodeName?: string): WorkflowNode | null {
+    // Try to find by ID first (exact match, no normalization needed for UUIDs)
     if (nodeId) {
       const nodeById = workflow.nodes.find(n => n.id === nodeId);
       if (nodeById) return nodeById;
     }
-    
+
+    // Try to find by name with normalization (handles special characters)
     if (nodeName) {
-      const nodeByName = workflow.nodes.find(n => n.name === nodeName);
+      const normalizedSearch = this.normalizeNodeName(nodeName);
+      const nodeByName = workflow.nodes.find(n =>
+        this.normalizeNodeName(n.name) === normalizedSearch
+      );
       if (nodeByName) return nodeByName;
     }
-    
-    // If nodeId is provided but not found, try treating it as a name
+
+    // Fallback: If nodeId provided but not found, try treating it as a name
+    // This allows operations to work with either IDs or names flexibly
     if (nodeId && !nodeName) {
-      const nodeByName = workflow.nodes.find(n => n.name === nodeId);
+      const normalizedSearch = this.normalizeNodeName(nodeId);
+      const nodeByName = workflow.nodes.find(n =>
+        this.normalizeNodeName(n.name) === normalizedSearch
+      );
       if (nodeByName) return nodeByName;
     }
-    
+
     return null;
   }