feat: add automatic word count and link validation to write operations

Add automatic word count and link validation to create_note, update_note,
and update_sections operations to provide immediate feedback on note content
quality and link integrity.

Features:
- Word counting excludes frontmatter and Obsidian comments, includes all
  other content (code blocks, inline code, headings, lists, etc.)
- Link validation checks wikilinks, heading links, and embeds
- Results categorized as: valid links, broken notes (note doesn't exist),
  and broken headings (note exists but heading missing)
- Detailed broken link info includes line number and context snippet
- Human-readable summary (e.g., "15 links: 12 valid, 2 broken notes, 1 broken heading")
- Opt-out capability via validateLinks parameter (default: true) for
  performance-critical operations

Implementation:
- New ContentUtils.countWords() for word counting logic
- Enhanced LinkUtils.validateLinks() for comprehensive link validation
- Updated create_note, update_note, update_sections to return wordCount
  and linkValidation fields
- Updated MCP tool descriptions to document new features and parameters
- update_note now returns structured JSON instead of simple success message

Response format changes:
- create_note: added wordCount and linkValidation fields
- update_note: changed to structured response with wordCount and linkValidation
- update_sections: added wordCount and linkValidation fields

Breaking changes:
- update_note response format changed from simple message to structured JSON

tests/parent-folder-detection.test.ts

@@ -1,6 +1,6 @@
 import { App } from 'obsidian';
 import { NoteTools } from '../src/tools/note-tools';
-import { createMockVaultAdapter, createMockFileManagerAdapter, createMockTFile, createMockTFolder } from './__mocks__/adapters';
+import { createMockVaultAdapter, createMockFileManagerAdapter, createMockMetadataCacheAdapter, createMockTFile, createMockTFolder } from './__mocks__/adapters';
 
 // Mock Obsidian API
 jest.mock('obsidian');
@@ -9,11 +9,13 @@ describe('Enhanced Parent Folder Detection', () => {
 	let noteTools: NoteTools;
 	let mockVault: ReturnType<typeof createMockVaultAdapter>;
 	let mockFileManager: ReturnType<typeof createMockFileManagerAdapter>;
+	let mockMetadata: ReturnType<typeof createMockMetadataCacheAdapter>;
 	let mockApp: App;
 
 	beforeEach(() => {
 		mockVault = createMockVaultAdapter();
 		mockFileManager = createMockFileManagerAdapter();
+		mockMetadata = createMockMetadataCacheAdapter();
 
 		// Create a minimal mock App that supports PathUtils
 		// Use a getter to ensure it always uses the current mock
@@ -25,7 +27,7 @@ describe('Enhanced Parent Folder Detection', () => {
 			}
 		} as any;
 
-		noteTools = new NoteTools(mockVault, mockFileManager, mockApp);
+		noteTools = new NoteTools(mockVault, mockFileManager, mockMetadata, mockApp);
 	});
 
 	describe('Explicit parent folder detection', () => {