Initial version of collation migration scripts.

docs/USAGE.md

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+# Usage – Data Copy (Variant B / Checkpointing)
+
+## Preconditions
+
+1. **Target database exists** (e.g. UTF-8 collation)
+2. **Target schema is deployed** (tables, constraints, indexes, views, procs, triggers, users/roles etc.)
+3. You can connect to the SQL Server instance with sufficient permissions.
+
+## Run
+
+Open `scripts/migrate_copy_checkpoint.sql` in SSMS.
+
+At the top configure:
+
+- `@SourceDb` (default: `sysdb_UTF8`)
+- `@TargetDb` (default: `sysdb_utf8_jr`)
+
+Optional behavior:
+
+- `@Mode`
+  - `RESUME` (default): skip tables already marked `DONE`
+  - `RESET`: reset state and rerun all tables
+
+- `@StopOnError`
+  - `1` (default): stop on first table error
+  - `0`: continue with next tables; check `dbo.MigrationState` afterwards
+
+- `@BatchSize`
+  - used for tables with `IDENTITY (int/bigint)` to copy in chunks
+
+Execute the script.
+
+## Monitoring
+
+The script prints progress like:
+
+- `... | TABLE_START | dbo.TableX`
+- `... | TABLE_DONE | dbo.TableX | Old=... New=...`
+- `... | TABLE_FAILED | dbo.TableX | Error ...`
+
+In target DB you also have:
+
+- `dbo.MigrationState` (table-level status)
+- `dbo.MigrationCopyLog` (append-only log)
+
+Useful queries:
+
+```sql
+USE sysdb_utf8_jr;
+SELECT * FROM dbo.MigrationState ORDER BY Status, TableSchema, TableName;
+SELECT TOP 200 * FROM dbo.MigrationCopyLog ORDER BY LogId DESC;
+```
+
+## Rerun behavior
+
+Each table is copied as:
+
+1. `DELETE FROM target.table`
+2. `INSERT INTO target.table SELECT ... FROM source.table`
+
+So reruns are safe. The checkpoint state enables resuming.