fix: instruct fix agent to write summaries in Simplified Chinese

[cwbcheng]

Problem

When PatchDeck resolves a review thread, the follow-up comment posted to GitHub mixes languages: the title line is Chinese (已在提交 \abc1234` 中处理。) but the agent summary is English, because the fix-agent prompt (buildAgentFixPrompt`) never told the agent which language to use. Only the code-owner fallback prompt contained the Chinese-language instruction.

Example posted on PR #434:

已在提交 45fca2f 中处理。

Restructured generate_installation_config.py so the --dry-run branch returns before assert_identity ... (English)

Fix

Add a language instruction to buildAgentFixPrompt so every summary block the fix agent emits (posted as follow-up comments on the PR) is written in Simplified Chinese, matching the existing Chinese templates and the code-owner fallback prompt.

Tests

• Extended the existing comment-task test to assert the fix-agent prompt instructs write every summary block in Simplified Chinese.
• Verified: node --import tsx --test server/babysitter.test.ts (110 tests pass), npm run check passes.

[jeremymcs]

Rebased onto main to clear the conflict — it is now conflict-free with green CI.

Flagging a scope question before this merges. The branch previously sat on top of feat: write GitHub comments and replies in Chinese, which is not in main and was not part of #163/#164/#165. I dropped that base commit as part of the rebase, so what remains is only your unique commit: a single line added to buildAgentFixPrompt instructing the agent to write every summary block in Simplified Chinese.

Applied to main as-is, that makes PatchDeck post Chinese summaries for every user, not just Chinese-language deployments — and main has no other Chinese-language strings, so it would be inconsistent on its own terms.

Mechanically it is ready. Whether it should merge upstream is a product call: if the goal is a fork customization it probably belongs in the fork, and if the goal is upstream language support it likely wants a config setting rather than a hardcoded prompt line.

Verified locally: npm run check, npm run test:all (788 tests), npx eslint . — all green.