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.

deploy/helm/sentry/templates/ingest.yaml

@@ -22,6 +22,18 @@ spec:
         - name: ingest
           image: "{{ .Values.ingest.image.repository }}:{{ .Values.ingest.image.tag }}"
           imagePullPolicy: {{ .Values.global.imagePullPolicy }}
+          {{- if and .Values.enterprise.enabled .Values.ingest.requireTenantCredential }}
+          # -mode=server only: this Deployment stops running the
+          # ClickHouse-writing consumer half (the default -mode=all)
+          # once per-tenant write-routing is on -- enterprise-ingest.yaml
+          # (below) takes over consuming sentry.logs.raw instead, so it
+          # can write each tenant's records to their own database rather
+          # than the one shared table ingest's own consumer always
+          # writes to. The agent-facing server half (PushBatch, tenant
+          # tagging via TenantResolver) keeps running here unconditionally
+          # either way -- only which process consumes the topic changes.
+          args: ["-mode=server"]
+          {{- end }}
           env:
             - name: REDPANDA_BROKERS
               value: "{{ .Release.Name }}-redpanda:9092"