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/types/mcp-types.ts

@@ -248,6 +248,8 @@ export interface UpdateSectionsResult {
 	versionId: string;
 	modified: number;
 	sectionsUpdated: number;
+	wordCount?: number;
+	linkValidation?: LinkValidationResult;
 }
 
 /**
@@ -260,6 +262,8 @@ export interface CreateNoteResult {
 	created: number;
 	renamed?: boolean;
 	originalPath?: string;
+	wordCount?: number;
+	linkValidation?: LinkValidationResult;
 }
 
 /**
@@ -305,6 +309,35 @@ export interface UnresolvedLink {
 	suggestions: string[];
 }
 
+/**
+ * Broken link information (note doesn't exist)
+ */
+export interface BrokenNoteLink {
+	link: string;
+	line: number;
+	context: string;
+}
+
+/**
+ * Broken heading link information (note exists but heading doesn't)
+ */
+export interface BrokenHeadingLink {
+	link: string;
+	line: number;
+	context: string;
+	note: string;
+}
+
+/**
+ * Link validation result for write operations
+ */
+export interface LinkValidationResult {
+	valid: string[];
+	brokenNotes: BrokenNoteLink[];
+	brokenHeadings: BrokenHeadingLink[];
+	summary: string;
+}
+
 /**
  * Result from validate_wikilinks operation
  */