Build per-tenant ClickHouse write-routing for ingest (Tantivy still deferred)

ingest tags every record with a tenant_id Kafka header (built previously),
but nothing consumed it to actually route the write. This closes that for
ClickHouse: enterprise/cmd/enterprise-ingest (a second binary, mirroring
enterprise-api) reuses ingest/consumer's own flush loop unchanged, with
enterprise/internal/chwriter.Registry -- a per-tenant clickhousewriter.Writer
registry -- swapped in as the writer. A batch pulled from the single shared
Redpanda topic can mix records from many tenants, so WriteBatch groups by
TenantID and dispatches each group to its own tenant's connection, fail-
closed on an empty or unrecognized tenant_id.

ingest/consumer and ingest/clickhousewriter move out of internal/ (same
reason api/internal/* moved earlier this phase: enterprise/ can't import
anything under another module's internal/). Their New() constructors now
take small local Config structs instead of ingest/internal/config types,
so enterprise/ doesn't need that import either.

Building this surfaced a real bug: tenantprovision.ProvisionClickHouse
only granted SELECT on a tenant's ClickHouse user, correct for chrunner's
read-only use but not enough for chwriter reusing the same credential to
write -- every real per-tenant write would have failed closed with a
permission error. Fixed by widening the grant to SELECT, INSERT; no
cross-tenant boundary is crossed by also allowing INSERT within a
tenant's own database.

Helm gates enterprise-ingest's Deployment on the same
ingest.requireTenantCredential flag that already gates tag validation --
write-routing is meaningless without tagging already being required, so
they're one decision, not two. docker-compose.yml's version is a
disclosed, weaker approximation: it can't achieve Helm's genuine
-mode=server/-mode=consumer split, so with the enterprise profile active
both ingest and enterprise-ingest independently consume every message
via different consumer groups -- harmless duplication for local
verification only.

Not built: Tantivy's independent Redpanda consumer (search/src/consumer.rs)
still doesn't read the tenant_id header at all -- every record still lands
in the one shared index regardless of tenant. Not run: the live-ClickHouse-
gated tests (chwriter's cross-tenant routing test, tenantprovision's INSERT
regression test) -- no Docker/database access in this environment; they're
correct Go that has never executed, disclosed as such in docs/security/
threat-model.md and docs/phase-4-runbook.md §14.

docker-compose.yml

@@ -365,6 +365,46 @@ services:
       timeout: 5s
       retries: 30
 
+  # Per-tenant write-routing for ingest (enterprise/internal/chwriter) --
+  # see enterprise/cmd/enterprise-ingest/main.go's doc comment. Unlike
+  # api/enterprise-api's COMPOSE_PROFILES trick, this is NOT wired to be
+  # mutually exclusive with `ingest`'s own consumer half in this file:
+  # `ingest` always runs -mode=all here regardless of profile (splitting
+  # its server/consumer halves into separate compose services isn't done
+  # -- real, disclosed scope, see /docs/phase-4-runbook.md), so with the
+  # "enterprise" profile active both this service AND ingest's own
+  # consumer independently read every message (different consumer
+  # groups) and write it -- ingest into the one shared `logs` table,
+  # this into each tenant's own database. Harmless duplication for local
+  # testing/verification purposes, not what a real deployment does (see
+  # deploy/helm/sentry's ingest.yaml/enterprise-ingest.yaml, which
+  # actually achieve exclusivity via -mode=server/-mode=consumer).
+  enterprise-ingest:
+    profiles: ["enterprise"]
+    build:
+      context: .
+      dockerfile: enterprise/cmd/enterprise-ingest/Dockerfile
+    container_name: sentry-enterprise-ingest
+    depends_on:
+      redpanda-provision:
+        condition: service_completed_successfully
+      clickhouse-migrate:
+        condition: service_completed_successfully
+      metadata-migrate:
+        condition: service_completed_successfully
+    environment:
+      REDPANDA_BROKERS: "redpanda:9092"
+      CLICKHOUSE_ADDR: "clickhouse:9000"
+      POSTGRES_ADDR: "metadata-postgres:5432"
+      POSTGRES_DATABASE: "sentry_metadata"
+      POSTGRES_USERNAME: "sentry"
+      POSTGRES_PASSWORD: "sentry-dev-only"
+    healthcheck:
+      test: ["CMD", "/enterprise-ingest", "-healthcheck"]
+      interval: 5s
+      timeout: 5s
+      retries: 30
+
   web:
     build:
       context: web