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>
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