Name agents by their first prompt line instead of an LLM summary (#1563)

* Name agents by their first prompt line instead of an LLM summary

The workspace title already captures the task; the LLM-generated agent
title just restated the same prompt. Drop the generator and keep the
provisional title (first prompt line), so the agent label stays
deterministic and explicit titles still win.

* Remove the no-op agent-title setting and leftover generator plumbing

Deleting the agent-title generator left its whole surface dangling: a
configurable "Agent titles" project setting that no longer did anything,
dead create-path plumbing, generator-only import/MCP deps, and the mock
provider's agent-title parser. Remove all of it, plus a dead test mock
and timing sleeps that guarded the deleted background job. Replace them
with a no-mock lifecycle test asserting the title stays the first prompt
line across create and settle.

Old paseo.json files with metadataGeneration.agentTitle still parse via
schema passthrough — see COMPAT(projectMetadataAgentTitle).

packages/app/src/i18n/resources/zh-CN.ts

@@ -1823,8 +1823,6 @@ export const zhCN: TranslationResources = {
       metadata: {
         title: "元数据生成",
         info: "注入到 Paseo 用来生成元数据的 AI prompts 中的 Project 专属指令，可用于强制执行团队约定，例如分支命名、提交风格或 PR 格式",
-        agentTitle: "Agent 标题",
-        agentTitlePlaceholder: "标题保持祈使句且不超过 40 个字符",
         branchName: "分支名称",
         branchNamePlaceholder: "分支以 feat/ 或 fix/ 开头，个人分支使用 mb/",
         commitMessage: "提交消息",