fix(alerting): use ALTER TABLE MODIFY SETTING to enable projections on executions ReplacingMergeTree

Investigated three approaches for CH 24.12:
- Inline SETTINGS on ADD PROJECTION: rejected (UNKNOWN_SETTING — not a query-level setting).
- ALTER TABLE MODIFY SETTING deduplicate_merge_projection_mode='rebuild': works; persists in
  table metadata across connection restarts; runs before ADD PROJECTION in the SQL script.
- Session-level JDBC URL param: not pursued (MODIFY SETTING is strictly better).

alerting_projections.sql now runs MODIFY SETTING before the two executions ADD PROJECTIONs.
AlertingProjectionsIT strengthened to assert all four projections (including alerting_app_status
and alerting_route_status on executions) exist after schema init.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cameleer-server-app/src/main/resources/clickhouse/alerting_projections.sql

@@ -1,12 +1,12 @@
 -- Alerting projections — additive and idempotent (IF NOT EXISTS).
 -- Safe to run on every startup alongside init.sql.
 --
--- NOTE: executions uses ReplacingMergeTree which requires deduplicate_merge_projection_mode='rebuild'
--- to support projections (ClickHouse 24.x). The ADD PROJECTION and MATERIALIZE statements for
--- executions are treated as best-effort by the schema initializer (non-fatal on failure).
--- logs and agent_metrics use plain MergeTree and always succeed.
+-- executions uses ReplacingMergeTree. ClickHouse 24.x requires deduplicate_merge_projection_mode='rebuild'
+-- for projections to work on ReplacingMergeTree. ALTER TABLE MODIFY SETTING persists the setting in
+-- table metadata (survives restarts) and runs before the ADD PROJECTION statements.
+-- logs and agent_metrics use plain MergeTree and do not need this setting.
 --
--- MATERIALIZE statements are also wrapped as non-fatal to handle empty tables in fresh deployments.
+-- MATERIALIZE statements are wrapped as non-fatal to handle empty tables in fresh deployments.
 
 -- Plain MergeTree tables: always succeed
 ALTER TABLE logs
@@ -17,7 +17,9 @@ ALTER TABLE agent_metrics
     ADD PROJECTION IF NOT EXISTS alerting_instance_metric
     (SELECT * ORDER BY (tenant_id, environment, instance_id, metric_name, collected_at));
 
--- ReplacingMergeTree tables: best-effort (requires deduplicate_merge_projection_mode='rebuild')
+-- ReplacingMergeTree: set table-level setting so ADD PROJECTION succeeds on any connection
+ALTER TABLE executions MODIFY SETTING deduplicate_merge_projection_mode = 'rebuild';
+
 ALTER TABLE executions
     ADD PROJECTION IF NOT EXISTS alerting_app_status
     (SELECT * ORDER BY (tenant_id, environment, application_id, status, start_time));