Add import/export and backup system (Milestone 8)

- Obsidian vault importer with wikilink → edge conversion
- Markdown folder importer with frontmatter parsing
- Markdown exporter with wikilinks and frontmatter
- JSON-LD linked data exporter
- Database backup/restore functionality
- CLI: import, backup, restore-backup, list-backups
- MCP tools: memory_import, memory_backup, memory_export_markdown, memory_export_jsonld

src/core/import/markdown.ts

@@ -0,0 +1,93 @@
+import * as fs from 'fs';
+import * as path from 'path';
+import { addNode } from '../store';
+import { NodeKind } from '../../types';
+
+export interface MarkdownImportOptions {
+  kind?: NodeKind;
+  tags?: string[];
+  dryRun?: boolean;
+}
+
+export interface MarkdownImportResult {
+  imported: number;
+  files: string[];
+}
+
+export async function importMarkdown(folderPath: string, options: MarkdownImportOptions = {}): Promise<MarkdownImportResult> {
+  const absPath = path.resolve(folderPath);
+
+  if (!fs.existsSync(absPath)) {
+    throw new Error(`Folder does not exist: ${absPath}`);
+  }
+
+  const files = findMarkdownFiles(absPath);
+  const defaultKind = options.kind || 'memory';
+  const defaultTags = options.tags || [];
+
+  if (options.dryRun) {
+    return {
+      imported: files.length,
+      files: files.map(f => path.relative(absPath, f)),
+    };
+  }
+
+  let imported = 0;
+  const importedFiles: string[] = [];
+
+  for (const file of files) {
+    const content = fs.readFileSync(file, 'utf-8');
+    const relativePath = path.relative(absPath, file);
+    const title = path.basename(file, '.md');
+
+    // Extract title from first H1 if present
+    const h1Match = content.match(/^#\s+(.+)$/m);
+    const nodeTitle = h1Match ? h1Match[1] : title;
+
+    // Remove the H1 from content if it was used as title
+    const nodeContent = h1Match ? content.replace(/^#\s+.+\n*/, '') : content;
+
+    await addNode({
+      kind: defaultKind,
+      title: nodeTitle,
+      content: nodeContent.trim(),
+      tags: ['imported', 'markdown', ...defaultTags],
+      metadata: {
+        importedFrom: 'markdown',
+        originalPath: relativePath,
+        importedAt: Date.now(),
+      },
+    });
+
+    imported++;
+    importedFiles.push(relativePath);
+  }
+
+  return {
+    imported,
+    files: importedFiles,
+  };
+}
+
+function findMarkdownFiles(dir: string): string[] {
+  const files: string[] = [];
+
+  function walk(currentDir: string) {
+    const entries = fs.readdirSync(currentDir, { withFileTypes: true });
+
+    for (const entry of entries) {
+      const fullPath = path.join(currentDir, entry.name);
+
+      if (entry.name.startsWith('.')) continue;
+
+      if (entry.isDirectory()) {
+        walk(fullPath);
+      } else if (entry.isFile() && entry.name.endsWith('.md')) {
+        files.push(fullPath);
+      }
+    }
+  }
+
+  walk(dir);
+  return files;
+}