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-core/src/streaming_parser.rs

@@ -587,7 +587,8 @@ Some text after"#;
             finished: true,
             tool_calls: None,
             usage: None,
-        stop_reason: None,
+            stop_reason: None,
+            tool_call_streaming: None,
         };
         
         let tools = parser.process_chunk(&chunk);