fix(n8n): resolve duplicate key constraint on tag_entity during workflow import

n8n import:workflow --separate imports each JSON file independently. All 4
workflows shared the same tags (parapharmacy, scraper), so the second import
tried to INSERT duplicate tag names, hitting the unique index on
tag_entity.name.

- Remove tags field from all 4 workflow JSON files (cosmetic, re-add via UI)
- Add cleanup-db.js to wipe workflow data before import
- Add --overwrite flag to import command as safety net
- Add cleanup-db.js volume mount to n8n-init container

n8n/cleanup-db.js

@@ -0,0 +1,46 @@
+#!/usr/bin/env node
+/**
+ * Clean n8n workflow data before fresh import to avoid constraint violations.
+ */
+let Client;
+try {
+  Client = require('/usr/local/lib/node_modules/n8n/node_modules/pg').Client;
+} catch {
+  Client = require('pg').Client;
+}
+
+const client = new Client({
+  host: process.env.DB_POSTGRESDB_HOST || 'postgres',
+  port: parseInt(process.env.DB_POSTGRESDB_PORT || '5432', 10),
+  database: process.env.DB_POSTGRESDB_DATABASE || 'farmafinder',
+  user: process.env.DB_POSTGRESDB_USER || 'farmafinder',
+  password: process.env.DB_POSTGRESDB_PASSWORD,
+});
+
+async function run() {
+  await client.connect();
+  console.log('[cleanup-db] Connected to PostgreSQL');
+
+  try {
+    for (const table of [
+      'workflows_tags',
+      'webhook_entity',
+      'execution_entity',
+      'workflow_statistics',
+      'workflow_archive',
+      'workflow_entity',
+    ]) {
+      try {
+        const r = await client.query(`DELETE FROM ${table}`);
+        if (r.rowCount > 0) console.log(`[cleanup-db] Deleted ${r.rowCount} rows from ${table}`);
+      } catch (e) {
+        if (e.code !== '42P01') console.error(`[cleanup-db] ${table}:`, e.message);
+      }
+    }
+    console.log('[cleanup-db] Done');
+  } finally {
+    await client.end();
+  }
+}
+
+run();