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/mcp/tool-docs/workflow_management/n8n-update-partial-workflow.ts

@@ -96,6 +96,8 @@ Add **ignoreErrors: true** to removeConnection operations to prevent failures wh
       'continueOnError breaks atomic guarantees - use with caution',
       'Order matters for dependent operations (e.g., must add node before connecting to it)',
       'Node references accept ID or name, but name must be unique',
+      'Node names with special characters (apostrophes, quotes) work correctly since v2.15.6 (Issue #270 fixed)',
+      'For best compatibility, prefer node IDs over names when dealing with special characters',
       'Use "updates" property for updateNode operations: {type: "updateNode", updates: {...}}',
       'cleanStaleConnections removes ALL broken connections - cannot be selective',
       'replaceConnections overwrites entire connections object - all previous connections lost'