feat: add goal mode

[yhw5231]

Closes #390

Summary

Adds an optional per-conversation goal mode for long-running Agent tasks. Goals persist with conversation history and expose lifecycle controls, pause/resume behavior, token/time usage, TodoWrite progress, provider recovery, and automatic continuation while the goal is active.

The follow-up fix also prevents completed or paused goals from steering later ordinary prompts, preserves /goal status and /goal help feedback after persistence, and excludes failed tool results from the no-progress detector.

Change scope

• Modules: agent-gui React runtime, chat history persistence, built-in goal tools, provider stream recovery
• Key paths:
  • crates/agent-gui/src/lib/chat/goal.ts
  • crates/agent-gui/src/lib/chat/conversation/
  • crates/agent-gui/src/lib/tools/goalTools.ts
  • crates/agent-gui/src/pages/chat/
  • crates/agent-gui/src-tauri/src/commands/history/chat_history/

Screenshots / preview

The preview shows the per-conversation goal-mode toggle in the chat composer.

Verification

• pnpm exec node --test test/chat/goal.test.mjs: 20 passed
• Goal runtime and queue regression tests: 16 passed
• pnpm exec tsc --noEmit: passed
• git diff --check: passed
• Full frontend suite: 1,424 passed; 5 unrelated baseline failures remain in MentionComposer function-extraction tests and provider preset synchronization.
• Rust tests were not run locally because cargo is not installed in the environment.

Pre-submit checklist

• A requirement issue is linked.
• Synced with the target branch; GitHub reports no merge conflicts.
• The change is focused, with no unrelated modifications to the implementation.
• No secrets, tokens, or personal data are included.
• User-facing documentation is updated.

[github-actions]

PR governance checks passed. Awaiting human review.