refactor: extract global styles and tokens (Task 2.1)

- Create styles/tokens.css with CSS custom properties and dark theme
- Create styles/global.css with resets, shell layout, and navigation
- Create styles/utilities.css with generic utilities and primitives
- Create styles/syntax-highlight.css with Prism.js theme
- Update main.tsx to import the 4 new style files
- Keep styles.css intact for backward compatibility

Quality gates: build (pass), lint (pass)
Refs: repo-restructure Task 2.1

apps/api/src/schemas/tool_instance.py

@@ -0,0 +1,17 @@
+"""Tool instance request/response schemas."""
+
+from pydantic import BaseModel, Field
+
+
+class CreateInstanceRequest(BaseModel):
+    """Request body for creating a tool instance."""
+
+    model_config = {"extra": "ignore"}
+
+    tool_type_id: str = Field(description="UUID of the tool type to instantiate")
+    display_name: str | None = Field(
+        default=None, description="Optional display name for the instance"
+    )
+    config_profile_id: str | None = Field(
+        default=None, description="Optional config profile ID to apply to the instance"
+    )