feat(alerting): ClickHouse projections for alerting read paths

Adds alerting_projections.sql with four projections (alerting_app_status,
alerting_route_status on executions; alerting_app_level on logs;
alerting_instance_metric on agent_metrics). ClickHouseSchemaInitializer now
runs both init.sql and alerting_projections.sql, with ADD PROJECTION and
MATERIALIZE treated as non-fatal — executions (ReplacingMergeTree) requires
deduplicate_merge_projection_mode=rebuild which is unavailable via JDBC pool.
MergeTree projections (logs, agent_metrics) always succeed and are asserted in IT.

Column names confirmed from init.sql: logs uses 'application' (not application_id),
agent_metrics uses 'collected_at' (not timestamp). All column names match the plan.

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

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

@@ -0,0 +1,33 @@
+-- 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.
+--
+-- MATERIALIZE statements are also wrapped as non-fatal to handle empty tables in fresh deployments.
+
+-- Plain MergeTree tables: always succeed
+ALTER TABLE logs
+    ADD PROJECTION IF NOT EXISTS alerting_app_level
+    (SELECT * ORDER BY (tenant_id, environment, application, level, timestamp));
+
+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')
+ALTER TABLE executions
+    ADD PROJECTION IF NOT EXISTS alerting_app_status
+    (SELECT * ORDER BY (tenant_id, environment, application_id, status, start_time));
+
+ALTER TABLE executions
+    ADD PROJECTION IF NOT EXISTS alerting_route_status
+    (SELECT * ORDER BY (tenant_id, environment, route_id, status, start_time));
+
+-- MATERIALIZE: best-effort on all tables (non-fatal if table is empty or already running)
+ALTER TABLE logs          MATERIALIZE PROJECTION alerting_app_level;
+ALTER TABLE agent_metrics MATERIALIZE PROJECTION alerting_instance_metric;
+ALTER TABLE executions    MATERIALIZE PROJECTION alerting_app_status;
+ALTER TABLE executions    MATERIALIZE PROJECTION alerting_route_status;