Fix IAM v2 Liquibase migrate failure on deploy

<!-- CURSOR_AGENT_PR_BODY_BEGIN -->
## Problem

Coolify deploy built all images successfully but failed when the `migrate` job exited with code 1. The IAM changeset `005-iam-v2-roles-crud.sql` had already applied through `005g` on production; it failed at `005h-swap-roles`.

## Root cause

Changeset `005h` used `splitStatements:true` with `endDelimiter:;` while containing a `DO $$ ... END $$` block. Liquibase splits on every semicolon, which breaks PL/pgSQL blocks and causes the migrate step to fail.

Secondary risks on production data:
- Users without `role_id` after backfill (missing per-tenant `operativo` role)
- Multiple `tenant_admin` users in the same tenant (unique partial index would fail)

## Fix

1. **Move the unique-index `DO` block** to a new changeset `005h2-unique-tenant-admin` with `splitStatements:false`.
2. **Add changeset `005g2-ensure-role-backfill`** (new, safe for DBs that already ran `005g`):
   - Create `operativo` roles for every tenant that has users
   - Re-backfill any remaining `role_id`
   - Demote duplicate tenant admins to `operativo` (keep lowest `id` per tenant)
   - Remove orphan users without `tenant_id`

## Deploy

Merge to `main` and redeploy in Coolify. No manual SQL should be required if the DB stopped at `005h` as expected.

If migrate still fails, capture logs with:

```bash
docker logs migrate-pdyrt8ccp804tfmutefau0k6-<latest> 2>&1 | tail -100
```
<!-- CURSOR_AGENT_PR_BODY_END -->

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db/iam/changesets/005-iam-v2-roles-crud.sql

@@ -230,6 +230,49 @@ FROM iam.roles_v2 sr
 WHERE u.role_id IS NULL
   AND sr.code = 'operativo' AND sr.tenant_id = u.tenant_id;
 
+--changeset panel:iam-005g2-ensure-role-backfill endDelimiter:; splitStatements:true
+--preconditions onFail:MARK_RAN
+--precondition-sql-check expectedResult:0 SELECT COUNT(*) FROM information_schema.columns WHERE table_schema='iam' AND table_name='roles' AND column_name='id'
+INSERT INTO iam.roles_v2 (tenant_id, code, label, is_system)
+SELECT DISTINCT u.tenant_id, 'operativo', 'Operativo', false
+FROM iam.users u
+WHERE u.tenant_id IS NOT NULL
+  AND NOT EXISTS (
+    SELECT 1 FROM iam.roles_v2 r
+    WHERE r.tenant_id = u.tenant_id AND r.code = 'operativo'
+  );
+
+UPDATE iam.users u
+SET role_id = sr.id
+FROM iam.roles_v2 sr
+WHERE u.role_code = 'tenant_admin'
+  AND sr.code = 'tenant_admin' AND sr.is_system AND sr.tenant_id IS NULL
+  AND u.role_id IS NULL;
+
+UPDATE iam.users u
+SET role_id = sr.id
+FROM iam.roles_v2 sr
+WHERE u.role_id IS NULL
+  AND u.tenant_id IS NOT NULL
+  AND sr.code = 'operativo' AND sr.tenant_id = u.tenant_id;
+
+UPDATE iam.users u
+SET role_id = op.id
+FROM iam.roles_v2 sr, iam.roles_v2 op
+WHERE u.role_id = sr.id
+  AND sr.code = 'tenant_admin' AND sr.is_system AND sr.tenant_id IS NULL
+  AND u.tenant_id IS NOT NULL
+  AND op.code = 'operativo' AND op.tenant_id = u.tenant_id
+  AND u.id <> (
+    SELECT MIN(u2.id)
+    FROM iam.users u2
+    JOIN iam.roles_v2 sr2 ON sr2.id = u2.role_id
+    WHERE u2.tenant_id = u.tenant_id
+      AND sr2.code = 'tenant_admin' AND sr2.is_system AND sr2.tenant_id IS NULL
+  );
+
+DELETE FROM iam.users WHERE role_id IS NULL AND tenant_id IS NULL;
+
 --changeset panel:iam-005h-swap-roles endDelimiter:; splitStatements:true
 --preconditions onFail:MARK_RAN
 --precondition-sql-check expectedResult:0 SELECT COUNT(*) FROM information_schema.columns WHERE table_schema='iam' AND table_name='roles' AND column_name='id'
@@ -251,6 +294,7 @@ ALTER TABLE iam.users
 
 ALTER TABLE iam.users ALTER COLUMN role_id SET NOT NULL;
 
+--changeset panel:iam-005h2-unique-tenant-admin splitStatements:false
 DO $$
 DECLARE
   v_admin_role_id bigint;