feat: add administrator repository (#11803)

Introduces the `administrators` relational table and repository layer
for the v3 backend, unifying instance, organization, project, and
project-grant membership into a single scoped model.

Closes #10220

## Changes

- **Domain**: `Administrator` struct, `AdministratorScope` enum,
`AdministratorRepository` interface with typed CRUD, column, condition,
and change helpers. Generated enumer and GoMock.
- **Migration** (`016`): `zitadel.administrators` table with a generated
`id`, scope-alignment check constraint, cascading foreign keys, and a
child `administrator_roles` table.
- **Repository**: CTE-based role mutations (`AddRole`, `RemoveRole`,
`SetRoles`) for atomicity. Roles aggregated via `ARRAY_AGG`.
- **Projection**: Event reducers for
`member.added/changed/removed/cascade_removed` across all four admin
scopes.
- **Fixes**: `Rows.Close()` error wrapping; `TextArray` nil-safe scan +
full `pgtype` array interface; `authorization` and `projectGrant` scan
helpers fixed for `ARRAY_AGG` under `database/sql`; removed unused `ctx`
parameter from `callReduce`.

---------

Co-authored-by: Marco Ardizzone <[email protected]>

backend/v3/storage/database/dialect/sql/rows.go

@@ -74,5 +74,5 @@ func (r *Rows) CollectExactlyOneRow(dest any) (err error) {
 // Close implements [database.Rows].
 // Subtle: this method shadows the method (Rows).Close of Rows.Rows.
 func (r *Rows) Close() error {
-	return r.Rows.Close()
+	return wrapError(r.Rows.Close())
 }