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.

enterprise/internal/ingestconfig/ingestconfig.go

@@ -0,0 +1,101 @@
+// Package ingestconfig loads enterprise-ingest's configuration from
+// environment variables -- same convention as every other Go service in
+// this repo. Named ingestconfig, not config, to avoid colliding with
+// enterprise/internal/config (enterprise-auth's own, differently-shaped
+// config) within the same module -- mirrors enterprise/internal/
+// apiconfig's own naming reasoning exactly.
+package ingestconfig
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type Config struct {
+	// HTTPListenAddr serves only /healthz -- this binary's actual job
+	// (Redpanda -> per-tenant ClickHouse) has no other HTTP surface,
+	// same "just enough for Docker's HEALTHCHECK" shape as every other
+	// binary in this repo's -healthcheck self-check mode.
+	HTTPListenAddr string
+	// ClickHouseAddr is the shared physical ClickHouse server's native
+	// address -- every tenant's connection (enterprise/internal/
+	// chwriter.Registry) dials this same address, just with different
+	// per-tenant credentials rbacstore already has on file from
+	// enterprise-api -provision-tenant. Mirrors apiconfig.Config.
+	// ClickHouseAddr's own doc comment.
+	ClickHouseAddr string
+	Postgres       PostgresConfig
+	Redpanda       RedpandaConfig
+	Batch          BatchConfig
+}
+
+type PostgresConfig struct {
+	Addr     string
+	Database string
+	Username string
+	Password string
+}
+
+type RedpandaConfig struct {
+	Brokers       []string
+	Topic         string
+	ConsumerGroup string
+}
+
+type BatchConfig struct {
+	MaxSize         int
+	FlushIntervalMS int
+}
+
+func Load() (Config, error) {
+	cfg := Config{
+		HTTPListenAddr: getenv("HTTP_LISTEN_ADDR", ":8084"),
+		ClickHouseAddr: getenv("CLICKHOUSE_ADDR", "localhost:9000"),
+		Postgres: PostgresConfig{
+			Addr:     getenv("POSTGRES_ADDR", "localhost:5432"),
+			Database: getenv("POSTGRES_DATABASE", "sentry_metadata"),
+			Username: getenv("POSTGRES_USERNAME", "sentry"),
+			Password: getenv("POSTGRES_PASSWORD", ""),
+		},
+		Redpanda: RedpandaConfig{
+			Brokers: strings.Split(getenv("REDPANDA_BROKERS", "localhost:9092"), ","),
+			// Same default topic ingest/internal/config uses -- this
+			// binary reads the identical shared sentry.logs.raw topic
+			// ingest/cmd/ingest's server half (agent-facing PushBatch)
+			// produces onto; there's no per-tenant topic, see
+			// ingest/internal/grpcserver's doc comment.
+			Topic: getenv("REDPANDA_TOPIC", "sentry.logs.raw"),
+			// A distinct consumer group from ingest/cmd/ingest's own
+			// default ("sentry-ingest") -- this binary and a
+			// single-tenant `ingest -mode=consumer` must never share a
+			// group (each message would only ever reach one of them,
+			// silently splitting traffic) even though in practice a
+			// real multi-tenant deployment runs this binary *instead
+			// of*, not alongside, `ingest -mode=consumer`.
+			ConsumerGroup: getenv("REDPANDA_CONSUMER_GROUP", "sentry-enterprise-ingest"),
+		},
+	}
+
+	maxSize, err := strconv.Atoi(getenv("CONSUMER_BATCH_MAX_SIZE", "500"))
+	if err != nil {
+		return Config{}, fmt.Errorf("CONSUMER_BATCH_MAX_SIZE: %w", err)
+	}
+	cfg.Batch.MaxSize = maxSize
+
+	flushMS, err := strconv.Atoi(getenv("CONSUMER_BATCH_FLUSH_INTERVAL_MS", "2000"))
+	if err != nil {
+		return Config{}, fmt.Errorf("CONSUMER_BATCH_FLUSH_INTERVAL_MS: %w", err)
+	}
+	cfg.Batch.FlushIntervalMS = flushMS
+
+	return cfg, nil
+}
+
+func getenv(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}