fix: backfill legacy Bedrock AI provider rows and stale model config strings (#26155)

Fixes CODAGT-548

Adds two idempotent startup backfills run after `newAPI():

- `BackfillBedrockProviderType`: promotes `ai_providers` rows from
`type=anthropic` with Bedrock settings to `type=bedrock`.
- `BackfillChatModelConfigProviderStrings`: fixes stale
`chat_model_configs.provider = "anthropic"` strings on rows whose linked
provider was just promoted.
- `UpdateAIProvider` query now also writes the `type` column, so the
fix persists on any subsequent PATCH.


> 🤖 Generated by Claude with oversight from a human.

coderd/database/dbmetrics/querymetrics.go

@@ -5,6 +5,7 @@ package dbmetrics
 
 import (
 	"context"
+	"database/sql"
 	"encoding/json"
 	"slices"
 	"time"
@@ -185,6 +186,14 @@ func (m queryMetricsStore) AutoArchiveInactiveChats(ctx context.Context, arg dat
 	return r0, r1
 }
 
+func (m queryMetricsStore) BackfillChatModelConfigProvider(ctx context.Context, arg database.BackfillChatModelConfigProviderParams) (sql.Result, error) {
+	start := time.Now()
+	r0, r1 := m.s.BackfillChatModelConfigProvider(ctx, arg)
+	m.queryLatencies.WithLabelValues("BackfillChatModelConfigProvider").Observe(time.Since(start).Seconds())
+	m.queryCounts.WithLabelValues(httpmw.ExtractHTTPRoute(ctx), httpmw.ExtractHTTPMethod(ctx), "BackfillChatModelConfigProvider").Inc()
+	return r0, r1
+}
+
 func (m queryMetricsStore) BackoffChatDiffStatus(ctx context.Context, arg database.BackoffChatDiffStatusParams) error {
 	start := time.Now()
 	r0 := m.s.BackoffChatDiffStatus(ctx, arg)