feat: real-time tool call streaming indicator with blinking UI

- Add ToolParsingHint enum (Detected/Active/Complete) for UI feedback
- New UiWriter methods: print_tool_streaming_hint(), print_tool_streaming_active()
- Refactor ConsoleUiWriter state to use atomics in ParsingHintState
- Add tool_call_streaming field to CompletionChunk for provider hints
- Anthropic provider sends streaming hints when tool name detected
- New streaming helpers: make_tool_streaming_hint(), make_tool_streaming_active()

Parser improvements:
- Add is_json_invalidated() to detect false positive tool patterns
- Fix tool result poisoning when file contents contain partial JSON
- Unescaped newlines in strings or prose after JSON invalidates detection

User sees ' ● tool_name |' immediately when tool call starts streaming,
with blinking indicator while args are received.

crates/g3-providers/src/openai.rs

@@ -158,6 +158,7 @@ impl OpenAIProvider {
                                         tool_calls,
                                         usage: accumulated_usage.clone(),
                                         stop_reason: None, // TODO: Extract from OpenAI response
+                                        tool_call_streaming: None,
                                     };
                                     let _ = tx.send(Ok(final_chunk)).await;
                                 }