style(desktop): render in-thread tool codicons as filled glyphs

Outline codicons read too thin at conversation-tool scale; a scoped
filled modifier thickens tool-row and code-card icons without changing
icon semantics elsewhere in the shell.

apps/desktop/src/components/assistant-ui/tool-fallback.tsx

@@ -136,7 +136,7 @@ function ToolGlyph({ copy, icon, status }: { copy: ToolStatusCopy; icon?: string
   const node = status ? (
     statusGlyph(status, copy)
   ) : icon ? (
-    <Codicon className="text-(--ui-text-tertiary)" name={icon} size="0.875rem" />
+    <Codicon className="text-(--ui-text-tertiary)" filled name={icon} size="0.875rem" />
   ) : null
 
   return node ? <span className={TOOL_HEADER_GLYPH_WRAP_CLASS}>{node}</span> : null

apps/desktop/src/components/chat/code-card.tsx

@@ -46,11 +46,12 @@ function CodeCardTitle({ className, children, ...props }: React.ComponentProps<'
   )
 }
 
-function CodeCardIcon({ className, ...props }: CodiconProps) {
+function CodeCardIcon({ className, filled = true, ...props }: CodiconProps) {
   return (
     <Codicon
       className={cn('shrink-0 text-[0.875rem] leading-none text-muted-foreground', className)}
       data-slot="code-card-icon"
+      filled={filled}
       {...props}
     />
   )

apps/desktop/src/components/ui/codicon.tsx

@@ -3,16 +3,24 @@ import type * as React from 'react'
 import { cn } from '@/lib/utils'
 
 export interface CodiconProps extends React.HTMLAttributes<HTMLElement> {
+  /** Thickens outline glyphs so they read as filled at small sizes (tool rows). */
+  filled?: boolean
   name: string
   size?: number | string
   spinning?: boolean
 }
 
-export function Codicon({ className, name, size, spinning, style, ...props }: CodiconProps) {
+export function Codicon({ className, filled, name, size, spinning, style, ...props }: CodiconProps) {
   return (
     <i
       aria-hidden="true"
-      className={cn('codicon', `codicon-${name}`, spinning && 'codicon-modifier-spin', className)}
+      className={cn(
+        'codicon',
+        `codicon-${name}`,
+        spinning && 'codicon-modifier-spin',
+        filled && 'codicon-modifier-filled',
+        className
+      )}
       style={{ fontSize: size, ...style }}
       {...props}
     />