refactor: simplify tool call display and path handling

- Remove displayName from tool calls, use name directly with icon
- Add medium font weight for tool call badges
- Strip workspace root from file paths at parsing level using Zod schema
- Add accentBorder to tool call badges and git diff file blocks
- Fix user message alignment and vertical spacing
- Deduplicate stripCwdPrefix into tool-call-parsers.ts

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/app/src/styles/theme.ts

@@ -179,6 +179,7 @@ const commonTheme = {
 
   fontWeight: {
     normal: "normal" as const,
+    medium: "500" as const,
     semibold: "600" as const,
     bold: "bold" as const,
   },