feat: upgrade TUI streaming to LangGraph streamEvents v3

[avoidwork]

Description

Upgrade the TUI streaming implementation to use LangGraph's streamEvents v3 API for real-time token-by-token rendering with tool call visibility. Replaces the old streamMode: "updates" approach with the newer event streaming API that provides typed projections for messages and tool lifecycle events. Text now renders incrementally as tokens arrive.

Type of Change

• New feature (non-breaking change which adds functionality)

Testing

• Replaced all 4 old streamMode: "updates" tests in tests/unit/react_agent.test.js with 8 new streamEvents v3 tests:
  • Token-by-token text delta streaming with accumulated display
  • Empty/whitespace token filtering (trim-based)
  • Tool event emission (tool_start, tool_end, tool_error, tool_event)
  • Fallback when no text content
  • Async iterable text handling on ChatModelStream
  • Text projection error handling (throws)
• Added 3 new TUI event dispatch tests in tests/unit/tui.test.js:
  • Text event dispatch from streamEvents callback
  • Tool end and tool error event formatting
  • Tool call display line formatting with newlines
• All 61 tests pass (18 agent + 43 TUI)
• Integration tests run as part of pre-commit hook

Coverage

• react.js: 100% line coverage (100.00 / 58.82% branch / 100.00% functions)
• Overall: 88.97% line coverage (up from 88.65%)
• All modified files have test coverage

Checklist

• npm run lint passes
• Tests pass with 100% line coverage on modified files
• No forbidden patterns used
• Conventional Commit style applied

Changes

src/agent/react.js

• callReactAgentStreaming uses agent.streamEvents({ version: "v3" })
• Iterates stream.messages for ChatModelStream instances
• Real incremental streaming: iterates chatMessage.text as async iterable, accumulating deltas and trimming before each callback
• Iterates raw ProtocolEvents to capture tools channel events
• New emitToolEvent() normalizes ProtocolEvents into typed callbacks

src/tui/app.js

• Unified event dispatch callback in handleChat processes all event types
• text events update streaming content with \u2588 cursor
• tool_end/tool_error events append formatted tool results to toolCallDisplay
• Tool call display persists after streaming completes

src/tui/conversationPanel.js

• Assistant messages with toolCallDisplay render tool results below content
• Dim/gray styled text for tool interactions

src/tui/messages.js

• Added getToolCallLines() helper function
• Updated Message typedef with toolCalls and toolCallDisplay fields