Add icons for the code, artifact, and read-document tools

Add Material Symbols-style SVG icons (terminal / document / document-scanner) for
code_executor, artifact_generator, and read_document so they render with an icon
like the other tools. The ToolIcon import.meta.glob resolves tool_<name>.svg by
backend tool name automatically — no registration needed.

frontend/src/assets/toolIcons/tool_artifact_generator.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" height="24px" viewBox="0 -960 960 960" width="24px" fill="currentColor"><path d="M320-240h320v-80H320v80Zm0-160h320v-80H320v80ZM240-80q-33 0-56.5-23.5T160-160v-640q0-33 23.5-56.5T240-880h320l240 240v480q0 33-23.5 56.5T720-80H240Zm280-520v-200H240v640h480v-440H520Z"/></svg>

frontend/src/assets/toolIcons/tool_code_executor.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" height="24px" viewBox="0 -960 960 960" width="24px" fill="currentColor"><path d="M160-160q-33 0-56.5-23.5T80-240v-480q0-33 23.5-56.5T160-800h640q33 0 56.5 23.5T880-720v480q0 33-23.5 56.5T800-160H160Zm0-80h640v-400H160v400Zm140-40-56-56 103-104-104-104 57-56 160 160-160 160Zm180 0v-80h200v80H480Z"/></svg>

frontend/src/assets/toolIcons/tool_read_document.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" height="24px" viewBox="0 -960 960 960" width="24px" fill="currentColor"><path d="M80-680v-200h200v80H160v120H80Zm600 0v-120H680v-80h200v200h-80ZM80-80v-200h80v120h120v80H80Zm600 0v-80h120v-120h80v200H680ZM280-280h400v-80H280v80Zm0-160h400v-80H280v80Z"/></svg>