feat(tui): debug-pane audit logging surface (v0.10.0)

Adds wire-level visibility appropriate for a debugging TUI. Every
SSE event arrival now lands as one debug-pane line; token-rate Text
and Thinking deltas get aggregated counters surfaced in a per-turn
summary instead of per-delta spam.

Audit surfaces added (all routed to the debug pane):
- per-event arrival: timestamp + event type + sse_id + event-specific
  summary for WorkerPhase / ToolStart / ToolResult / TextBoundary /
  Done / Error / Cancelled
- turn-summary at terminal events: text_deltas / text_bytes /
  thinking_deltas / thinking_bytes / elapsed_ms
- app-level state-machine transitions via new RatatoskrApp._transition
  helper (idle → streaming → cancelling → idle, with reason)
- worker_spawn line at on_input_submitted with content_len
- ctrl_c / ctrl_d audit lines documenting action + exit code
- cancel POST lifecycle: _cancel_via_sse takes an optional audit
  callback and emits issued / ok / failed lines
- app_mounted bootstrap line at on_mount (server + agent + session
  tail + raw + end_user_id)
- wire-error exception class + body audit at _stream_turn_worker

Helpers:
- TuiPresenterState: text_delta_count / text_byte_count /
  thinking_delta_count / thinking_byte_count / turn_start_ts
- module-level _ts() + _audit_line() + RatatoskrApp._audit() /
  _transition()

Tests: 6 new test cases lock in audit-line shape, turn-summary
aggregation, cancel-POST lifecycle callback, and the silence of
per-Text-delta debug writes.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "ratatoskr"
-version = "0.9.0"
+version = "0.10.0"
 description = "Worldtree Conversation API debug TUI — multi-pane observability dashboard"
 readme = "README.md"
 requires-python = ">=3.12"