chore: rename user-facing AI Bridge strings to AI Gateway (#26700)

Rename user-facing "AI Bridge" strings to "AI Gateway" in deployment
config, RBAC display names, log messages, error strings, docs style
guide, and Grafana dashboard README.

Deprecated option names and descriptions (the `--aibridge-*` block) are
intentionally kept as "AI Bridge". The `Name` field cannot be renamed
because `serpent` uses it as a unique key during JSON serialization;
duplicating names causes `UnmarshalJSON` failures (e.g. in the support
bundle). Descriptions also stay as "AI Bridge" to avoid confusion
between the deprecated and primary options.

Refs https://linear.app/codercom/issue/AIGOV-226

> Generated with the assistance of Coder Agents (@ssncferreira)

coderd/ai_providers_migrate.go

@@ -143,7 +143,7 @@ func SeedAIProvidersFromEnv(
 				if existingHash == dp.Hash {
 					continue
 				}
-				return xerrors.Errorf("AI provider %q already exists in the database and differs from the current environment configuration; update the provider through the API or remove the CODER_AIBRIDGE_* env vars to stop seeding it", dp.Name)
+				return xerrors.Errorf("AI provider %q already exists in the database and differs from the current environment configuration; update the provider through the API or remove the CODER_AIBRIDGE_* (legacy) / CODER_AI_GATEWAY_* env vars to stop seeding it", dp.Name)
 			}
 
 			row, err := tx.InsertAIProvider(sysCtx, database.InsertAIProviderParams{

coderd/coderd.go

@@ -625,7 +625,7 @@ func New(options *Options) *API {
 	// Seed the AI Bridge model price table from the embedded price book.
 	//nolint:gocritic // Startup seeder needs to run as aibridge context.
 	if err := prices.Seed(dbauthz.AsAIBridged(ctx), options.Database); err != nil {
-		options.Logger.Error(ctx, "failed to seed AI Bridge prices; cost tracking may use stale prices", slog.Error(err))
+		options.Logger.Error(ctx, "failed to seed AI Gateway prices; cost tracking may use stale prices", slog.Error(err))
 	}
 
 	// AGPL uses a no-op build usage checker as there are no license

coderd/database/dbauthz/dbauthz.go

@@ -638,12 +638,12 @@ var (
 	// See aibridged package.
 	subjectAibridged = rbac.Subject{
 		Type:         rbac.SubjectAibridged,
-		FriendlyName: "AI Bridge Daemon",
+		FriendlyName: "AI Gateway Daemon",
 		ID:           uuid.Nil.String(),
 		Roles: rbac.Roles([]rbac.Role{
 			{
 				Identifier:  rbac.RoleIdentifier{Name: "aibridged"},
-				DisplayName: "AI Bridge Daemon",
+				DisplayName: "AI Gateway Daemon",
 				Site: rbac.Permissions(map[string][]policy.Action{
 					rbac.ResourceUser.Type: {
 						policy.ActionRead,         // Required to validate API key owner is active.

coderd/telemetry/telemetry.go

@@ -774,7 +774,7 @@ func (r *remoteReporter) createSnapshot() (*Snapshot, error) {
 	eg.Go(func() error {
 		summaries, err := r.generateAIBridgeInterceptionsSummaries(ctx)
 		if err != nil {
-			return xerrors.Errorf("generate AI Bridge interceptions telemetry summaries: %w", err)
+			return xerrors.Errorf("generate AI Gateway interceptions telemetry summaries: %w", err)
 		}
 		snapshot.AIBridgeInterceptionsSummaries = summaries
 		return nil
@@ -878,7 +878,7 @@ func (r *remoteReporter) generateAIBridgeInterceptionsSummaries(ctx context.Cont
 		return nil, nil
 	}
 	if err != nil {
-		return nil, xerrors.Errorf("insert AI Bridge interceptions telemetry lock (period_ending_at=%q): %w", endedAtBefore, err)
+		return nil, xerrors.Errorf("insert AI Gateway interceptions telemetry lock (period_ending_at=%q): %w", endedAtBefore, err)
 	}
 
 	// List the summary categories that need to be calculated.
@@ -887,7 +887,7 @@ func (r *remoteReporter) generateAIBridgeInterceptionsSummaries(ctx context.Cont
 		EndedAtBefore: endedAtBefore, // exclusive
 	})
 	if err != nil {
-		return nil, xerrors.Errorf("list AI Bridge interceptions telemetry summaries (startedAtAfter=%q, endedAtBefore=%q): %w", endedAtAfter, endedAtBefore, err)
+		return nil, xerrors.Errorf("list AI Gateway interceptions telemetry summaries (startedAtAfter=%q, endedAtBefore=%q): %w", endedAtAfter, endedAtBefore, err)
 	}
 
 	// Calculate and convert the summaries for all categories.
@@ -906,7 +906,7 @@ func (r *remoteReporter) generateAIBridgeInterceptionsSummaries(ctx context.Cont
 				EndedAtBefore: endedAtBefore,
 			})
 			if err != nil {
-				return xerrors.Errorf("calculate AI Bridge interceptions telemetry summary (provider=%q, model=%q, client=%q, startedAtAfter=%q, endedAtBefore=%q): %w", category.Provider, category.Model, category.Client, endedAtAfter, endedAtBefore, err)
+				return xerrors.Errorf("calculate AI Gateway interceptions telemetry summary (provider=%q, model=%q, client=%q, startedAtAfter=%q, endedAtBefore=%q): %w", category.Provider, category.Model, category.Client, endedAtAfter, endedAtBefore, err)
 			}
 
 			// Double check that at least one interception was found in the