fix(webapp): gate bedrock head-start on AWS_REGION only

Author: kathiekiwi

apps/webapp/app/env.server.ts

@@ -175,7 +175,6 @@ const EnvironmentSchema = z
     // DASHBOARD_AGENT_MODEL_PROVIDER=bedrock; default path stays Anthropic). The
     // provider resolves credentials itself, so only the region is read here.
     AWS_REGION: z.string().optional(),
-    AWS_DEFAULT_REGION: z.string().optional(),
     AWS_ACCESS_KEY_ID: z.string().optional(),
     AWS_SECRET_ACCESS_KEY: z.string().optional(),
     AWS_SESSION_TOKEN: z.string().optional(),

apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.dashboard-agent.ts

@@ -332,7 +332,7 @@ export const action = async ({ request, params }: ActionFunctionArgs) => {
       const repoSnapshot = await resolveDashboardAgentRepoSnapshot(project.id);
       const headStarted =
         dashboardAgentProvider() === "bedrock"
-          ? Boolean(env.AWS_REGION || env.AWS_DEFAULT_REGION)
+          ? Boolean(env.AWS_REGION)
           : Boolean(env.ANTHROPIC_API_KEY);
 
       // The lookups and the mint all run before the chat row exists, so a failure here can't