bug+feat: spinner freeze during tool execution + better spinner style with animated dots

[VforVitorio]

Bug: spinner freezes during tool execution

model.act() calls tool functions synchronously inside the coroutine. The asyncio event loop is fully blocked during the tool call — the keepalive task cannot run. Affects list_files, run_shell, read_file, etc.

The asyncio keepalive only helps during prefill (HTTP await). Cannot move model.act() to a background thread without event loop mismatch (AsyncTaskManager is bound to the main loop).

Consolidates #39.

Feat: better spinner style

Replace the current static thinking… text with:

1. Animated dots cycling on the text: thinking. → thinking.. → thinking... → repeat (every ~0.3 s via the keepalive tick)
2. State machine labels that reflect what the model is actually doing (see issue feat: dynamic status label in spinner — thinking / working / finishing #45)
3. Spinner style — consider circleHalves (◐◓◑◒) or keeping dots but with full ACCENT violet on both the spinner char and the text

Steps to reproduce freeze

1. Run lmcode with a model loaded
2. Ask: lista los archivos de src
3. Observe spinner freezes while list_files executes

🤖 Generated with Claude Code

[VforVitorio]

Spinner style changed to circleHalves (◐◓◑◒) — subtler than dots and pairs well with the animated text labels. The freeze itself remains a known SDK limitation (model.act() calls tools synchronously).