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-planner/src/llm.rs

@@ -292,6 +292,14 @@ impl g3_core::ui_writer::UiWriter for PlannerUiWriter {
         // The "Thinking..." status was causing overwrites
     }
     
+    fn print_tool_streaming_hint(&self, _tool_name: &str) {
+        // No-op for planner - we don't show streaming hints
+    }
+
+    fn print_tool_streaming_active(&self) {
+        // No-op for planner - we don't show streaming hints
+    }
+
     fn flush(&self) {
         use std::io::Write;
         std::io::stdout().flush().ok();