fix: combine ClickHouse app user grants into single query (HDX-3832) (#198)

## Summary
- The ClickHouse operator only applies the first `grants` entry when
multiple are listed separately
- The `app` user was missing `SELECT ON system.*` and `SELECT ON
default.*` permissions — only `GRANT SHOW ON *.*` was applied
- Combined all grants into a single query, matching the pattern that
works for the `otelcollector` user

## Test plan
- [x] `helm unittest charts/clickstack` — all 146 tests pass
- [x] Deploy and verify with `SHOW GRANTS FOR app` in ClickHouse —
should show all 3 permissions

Linear: HDX-3832

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wrn14897

.changeset/better-otters-train.md

@@ -0,0 +1,5 @@
+---
+"helm-charts": patch
+---
+
+fix: combine ClickHouse app user grants into single query

charts/clickstack/values.yaml

@@ -305,9 +305,7 @@ clickhouse:
               password: '{{ .Values.hyperdx.secrets.CLICKHOUSE_APP_PASSWORD }}'
               profile: default
               grants:
-                - query: "GRANT SHOW ON *.*"
-                - query: "GRANT SELECT ON system.*"
-                - query: "GRANT SELECT ON default.*"
+                - query: "GRANT SHOW ON *.*, SELECT ON system.*, SELECT ON default.*"
             otelcollector:
               password: '{{ .Values.hyperdx.secrets.CLICKHOUSE_PASSWORD }}'
               profile: default