Improve mt migration process

backend/alembic/README.md

@@ -20,3 +20,44 @@ To run all un-applied migrations:
 To undo migrations:
 `alembic downgrade -X`
 where X is the number of migrations you want to undo from the current state
+
+### Multi-tenant migrations
+
+For multi-tenant deployments, you can use additional options:
+
+**Upgrade all tenants:**
+```bash
+alembic -x upgrade_all_tenants=true upgrade head
+```
+
+**Upgrade specific schemas:**
+```bash
+# Single schema
+alembic -x schemas=tenant_12345678-1234-1234-1234-123456789012 upgrade head
+
+# Multiple schemas (comma-separated)
+alembic -x schemas=tenant_12345678-1234-1234-1234-123456789012,public,another_tenant upgrade head
+```
+
+**Upgrade tenants within an alphabetical range:**
+```bash
+# Upgrade tenants 100-200 when sorted alphabetically (positions 100 to 200)
+alembic -x upgrade_all_tenants=true -x tenant_range_start=100 -x tenant_range_end=200 upgrade head
+
+# Upgrade tenants starting from position 1000 alphabetically
+alembic -x upgrade_all_tenants=true -x tenant_range_start=1000 upgrade head
+
+# Upgrade first 500 tenants alphabetically
+alembic -x upgrade_all_tenants=true -x tenant_range_end=500 upgrade head
+```
+
+**Continue on error (for batch operations):**
+```bash
+alembic -x upgrade_all_tenants=true -x continue=true upgrade head
+```
+
+The tenant range filtering works by:
+1. Sorting tenant IDs alphabetically
+2. Using 1-based position numbers (1st, 2nd, 3rd tenant, etc.)
+3. Filtering to the specified range of positions
+4. Non-tenant schemas (like 'public') are always included