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

src/utils/content-utils.ts

@@ -0,0 +1,42 @@
+import { FrontmatterUtils } from './frontmatter-utils';
+
+/**
+ * Utility class for content analysis and manipulation
+ */
+export class ContentUtils {
+	/**
+	 * Count words in content, excluding frontmatter and Obsidian comments
+	 * Includes all other content: headings, paragraphs, lists, code blocks, inline code
+	 *
+	 * @param content The full markdown content to analyze
+	 * @returns Word count (excludes frontmatter and Obsidian comments only)
+	 */
+	static countWords(content: string): number {
+		// Extract frontmatter to get content without it
+		const { contentWithoutFrontmatter } = FrontmatterUtils.extractFrontmatter(content);
+
+		// Remove Obsidian comments (%% ... %%)
+		// Handle both single-line and multi-line comments
+		const withoutComments = this.removeObsidianComments(contentWithoutFrontmatter);
+
+		// Split by whitespace and count non-empty tokens
+		const words = withoutComments
+			.split(/\s+/)
+			.filter(word => word.trim().length > 0);
+
+		return words.length;
+	}
+
+	/**
+	 * Remove Obsidian comments from content
+	 * Handles both %% single line %% and multi-line comments
+	 *
+	 * @param content Content to process
+	 * @returns Content with Obsidian comments removed
+	 */
+	private static removeObsidianComments(content: string): string {
+		// Remove Obsidian comments: %% ... %%
+		// Use non-greedy match to handle multiple comments
+		return content.replace(/%%[\s\S]*?%%/g, '');
+	}
+}