Parameterize sys prompt (#1082)

<!-- This is an auto-generated description by cubic. -->

## Summary by cubic
Parameterized the system prompt and tokenized it in e2e dumps to make
snapshots smaller and stable. No runtime behavior changes; future prompt
edits won’t churn tests.

- **Refactors**
- Exported BUILD_SYSTEM_PREFIX and BUILD_SYSTEM_POSTFIX from
system_prompt.ts.
- Updated test_helper to replace the full prompt with
${BUILD_SYSTEM_PREFIX}/${BUILD_SYSTEM_POSTFIX} tokens in message dumps.
- Regenerated e2e snapshots to use tokens, reducing ~270 lines per
snapshot.

<!-- End of auto-generated description by cubic. -->

e2e-tests/helpers/test_helper.ts

@@ -6,6 +6,10 @@ import path from "path";
 import os from "os";
 import { execSync } from "child_process";
 import { generateAppFilesSnapshotData } from "./generateAppFilesSnapshotData";
+import {
+  BUILD_SYSTEM_POSTFIX,
+  BUILD_SYSTEM_PREFIX,
+} from "@/prompts/system_prompt";
 
 const showDebugLogs = process.env.DEBUG_LOGS === "true";
 
@@ -1144,6 +1148,8 @@ function prettifyDump(
       const content = Array.isArray(message.content)
         ? JSON.stringify(message.content)
         : message.content
+            .replace(BUILD_SYSTEM_PREFIX, "\n${BUILD_SYSTEM_PREFIX}")
+            .replace(BUILD_SYSTEM_POSTFIX, "${BUILD_SYSTEM_POSTFIX}")
             // Normalize line endings to always use \n
             .replace(/\r\n/g, "\n")
             // We remove package.json because it's flaky.