feat: implement concrete adapter classes

Add VaultAdapter, MetadataCacheAdapter, and FileManagerAdapter as
pass-through wrappers for Obsidian API objects.

src/adapters/vault-adapter.ts

@@ -0,0 +1,41 @@
+import { Vault, TAbstractFile, TFile, TFolder, DataWriteOptions } from 'obsidian';
+import { IVaultAdapter } from './interfaces';
+
+export class VaultAdapter implements IVaultAdapter {
+	constructor(private vault: Vault) {}
+
+	async read(file: TFile): Promise<string> {
+		return this.vault.read(file);
+	}
+
+	stat(file: TAbstractFile): { ctime: number; mtime: number; size: number } | null {
+		if (file instanceof TFile) {
+			return file.stat;
+		}
+		return null;
+	}
+
+	getAbstractFileByPath(path: string): TAbstractFile | null {
+		return this.vault.getAbstractFileByPath(path);
+	}
+
+	getMarkdownFiles(): TFile[] {
+		return this.vault.getMarkdownFiles();
+	}
+
+	getRoot(): TFolder {
+		return this.vault.getRoot();
+	}
+
+	async process(file: TFile, fn: (data: string) => string, options?: DataWriteOptions): Promise<string> {
+		return this.vault.process(file, fn, options);
+	}
+
+	async createFolder(path: string): Promise<void> {
+		await this.vault.createFolder(path);
+	}
+
+	async create(path: string, data: string): Promise<TFile> {
+		return this.vault.create(path, data);
+	}
+}