Revert "Set EVENT_REPOSITORY_DEFAULT_STORE default to clickhouse_v2 (#2879)"

This reverts commit 495a253.

Restores EVENT_REPOSITORY_DEFAULT_STORE default from "clickhouse_v2" back to "postgres".

Co-authored-by: ericallam <534+ericallam@users.noreply.github.com>

Author: Copilot

apps/webapp/app/env.server.ts

@@ -1223,7 +1223,7 @@ const EnvironmentSchema = z
     EVENT_REPOSITORY_CLICKHOUSE_ROLLOUT_PERCENT: z.coerce.number().optional(),
     EVENT_REPOSITORY_DEFAULT_STORE: z
       .enum(["postgres", "clickhouse", "clickhouse_v2"])
-      .default("clickhouse_v2"),
+      .default("postgres"),
     EVENT_REPOSITORY_DEBUG_LOGS_DISABLED: BoolEnv.default(false),
     EVENTS_CLICKHOUSE_MAX_TRACE_SUMMARY_VIEW_COUNT: z.coerce.number().int().default(25_000),
     EVENTS_CLICKHOUSE_MAX_TRACE_DETAILED_SUMMARY_VIEW_COUNT: z.coerce.number().int().default(5_000),