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/screens/project-settings-screen.tsx

@@ -58,12 +58,6 @@ interface MetadataPromptField {
 }
 
 const METADATA_PROMPT_FIELDS: Record<MetadataPromptKey, MetadataPromptField> = {
-  agentTitle: {
-    titleKey: "settings.project.metadata.agentTitle",
-    placeholderKey: "settings.project.metadata.agentTitlePlaceholder",
-    sectionTestID: "metadata-prompt-agent-title-section",
-    inputTestID: "metadata-prompt-agent-title-input",
-  },
   branchName: {
     titleKey: "settings.project.metadata.branchName",
     placeholderKey: "settings.project.metadata.branchNamePlaceholder",