chore: increase SOURCEBOT_CHAT_MAX_STEP_COUNT default to 100

Allows chat sessions to perform more autonomous steps before stopping.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: brendan-kellam

packages/shared/src/env.server.ts

@@ -238,7 +238,7 @@ const options = {
         AWS_REGION: z.string().optional(),
 
         SOURCEBOT_CHAT_MODEL_TEMPERATURE: numberSchema.default(0.3),
-        SOURCEBOT_CHAT_MAX_STEP_COUNT: numberSchema.default(20),
+        SOURCEBOT_CHAT_MAX_STEP_COUNT: numberSchema.default(100),
 
         DEBUG_WRITE_CHAT_MESSAGES_TO_FILE: booleanSchema.default('false'),