feat: Add mouse text selection auto-copy to clipboard in TUI

Enable native text selection across tool components and agent messages
with automatic clipboard copy, toast notification, and decorative icon
stripping. Replace Padding wrappers with Text to support selection
across multiple renderables.

strix/agents/state.py

@@ -43,7 +43,9 @@ class AgentState(BaseModel):
         self.iteration += 1
         self.last_updated = datetime.now(UTC).isoformat()
 
-    def add_message(self, role: str, content: Any, thinking_blocks: list[dict[str, Any]] | None = None) -> None:
+    def add_message(
+        self, role: str, content: Any, thinking_blocks: list[dict[str, Any]] | None = None
+    ) -> None:
         message = {"role": role, "content": content}
         if thinking_blocks:
             message["thinking_blocks"] = thinking_blocks