feat: Phase 3 - Discovery Endpoints (stat and exists tools)

- Add stat tool for detailed file/folder metadata
- Add exists tool for fast path existence checking
- Add StatResult and ExistsResult type definitions
- Implement stat() and exists() methods in VaultTools
- Register both tools in ToolRegistry with complete schemas
- Update version to 2.1.0
- Update ROADMAP.md to mark Phase 3 complete
- Update CHANGELOG.md with Phase 3 release notes
- Add IMPLEMENTATION_NOTES_PHASE3.md documentation
- Clean up old phase documentation files

src/types/mcp-types.ts

@@ -107,3 +107,17 @@ export interface SearchResult {
 	filesSearched: number;
 	filesWithMatches: number;
 }
+
+// Phase 3: Discovery Endpoint Types
+export interface StatResult {
+	path: string;
+	exists: boolean;
+	kind?: ItemKind;
+	metadata?: FileMetadata | DirectoryMetadata;
+}
+
+export interface ExistsResult {
+	path: string;
+	exists: boolean;
+	kind?: ItemKind;
+}