Add streaming token count updates via --include-partial-messages

[zhubert]

Summary

Enables real-time token count updates during Claude streaming responses by adding the --include-partial-messages flag to the Claude CLI invocation and parsing the resulting stream events.

Changes

• Add --include-partial-messages flag to all Claude CLI command argument builders (resume, fork, new session)
• Add streamEvent struct to parse the event payload in stream_event messages
• Implement handleStreamEventTokens() to extract and emit token counts from message_start and message_delta events
• Add parseStreamEvent() to handle content extraction from various stream event types (text deltas, tool use, etc.)
• Add comprehensive tests for stream event parsing

Test plan

• Run go test ./internal/claude/... to verify the new parsing tests pass
• Start a session and observe that token counts update incrementally during streaming (rather than only at the end)
• Verify text streaming still works correctly with the new event parsing

[github-actions]

🔍 Deadcode Analysis

✅ No unreachable functions detected. Nice work keeping the codebase clean!