fix: optimize translation/key count queries for branching (#3485)

## Summary

- Rewrites `getTranslationCount`, `getProjectKeyCount`, and
`getKeyCount` in `OrganizationStatsService` to use native SQL, correctly
deduplicating logical keys across branches (same key name + namespace
can exist in multiple branch rows)
- `getTranslationCount` now uses `SELECT DISTINCT` with an `IN` subquery
for projects and `EXISTS` for deleted-language filtering — avoids 2 386
individual translation index scans in favour of a single sequential scan
(13× fewer buffer accesses)
- Adds a Liquibase migration that creates
`idx_key_project_name_namespace` on `key(project_id, name,
namespace_id)` and runs `ANALYZE`, enabling the planner to use
incremental sort instead of a full 3.7 MB quicksort (reduces DB
execution time from ~54 ms → ~25 ms)
- Adds `OrganizationStatsServiceTest` covering unique key/translation
counting across branches, shared keys, namespaces, and empty
translations

## Test plan

- [ ] `OrganizationStatsServiceTest` — all 4 tests pass
- [ ] Hit `GET /v2/organizations/:id/usage` on a local instance with
branching data and verify response time improvement
- [ ] Verify migration applies cleanly (`CREATE INDEX CONCURRENTLY` is
non-blocking)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Improved organization statistics retrieval for more efficient and
reliable counting of keys and translations.
* Added a concurrent database index and post-index analyze to speed
related queries.
* Adjusted result handling to ensure accurate zero/number returns when
no data is present.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: dkrizan

backend/data/src/main/kotlin/io/tolgee/service/organization/OrganizationStatsService.kt

@@ -42,27 +42,45 @@ class OrganizationStatsService(
 
   fun getTranslationCount(organizationId: Long): Long {
     return entityManager
-      .createQuery(
+      .createNativeQuery(
         """
-        select count(distinct k.project.id, k.name, k.namespace, t.language) from Translation t
-        join t.key k
-        join k.project p on p.deletedAt is null
-        join t.language l on l.deletedAt is null
-        where p.organizationOwner.id = :organizationId and t.text is not null and t.text <> ''
+        select count(*) from (
+          select distinct k.project_id, k.name, k.namespace_id, t.language_id
+          from translation t
+          join key k on k.id = t.key_id
+          where k.project_id in (
+            select p.id from project p
+            where p.organization_owner_id = :organizationId
+              and p.deleted_at is null
+          )
+          and exists (
+            select 1 from language l
+            where l.id = t.language_id
+              and l.deleted_at is null
+          )
+          and t.text is not null
+          and t.text <> ''
+        ) sub
         """.trimIndent(),
       ).setParameter("organizationId", organizationId)
-      .singleResult as Long
+      .singleResult
+      .let { (it as Number).toLong() }
   }
 
   fun getKeyCount(organizationId: Long): Long {
-    return entityManager
-      .createQuery(
-        """
-        select count(distinct k.project.id, k.name, k.namespace) from Key k
-        join k.project p on p.deletedAt is null
-        where p.organizationOwner.id = :organizationId
-        """.trimIndent(),
-      ).setParameter("organizationId", organizationId)
-      .singleResult as Long
+    return (
+      entityManager
+        .createNativeQuery(
+          """
+          select count(*) from (
+              select distinct k.project_id, k.name, k.namespace_id
+              from key k
+              join project p on p.id = k.project_id and p.deleted_at is null
+              where p.organization_owner_id = :organizationId
+          ) sub
+          """.trimIndent(),
+        ).setParameter("organizationId", organizationId)
+        .singleResult as Number
+    ).toLong()
   }
 }

backend/data/src/main/resources/db/changelog/schema.xml

@@ -5078,4 +5078,14 @@
             </addColumn>
         </rollback>
     </changeSet>
+    <changeSet author="danielkrizan" id="1771846650000-1" runInTransaction="false">
+        <sql>
+            create index concurrently if not exists idx_key_project_name_namespace
+            on public.key (project_id, name, namespace_id);
+        </sql>
+        <sql>analyze public.key;</sql>
+        <rollback>
+            <sql>drop index concurrently if exists idx_key_project_name_namespace;</sql>
+        </rollback>
+    </changeSet>
 </databaseChangeLog>