Syntax-highlight Edit, Write, and Read tool calls (#1218)

Highlighting reuses the existing code-block tokenizer and LRU cache, runs
lazily on expand, and falls back to plain text above a size cap so a large
Read can't stall the main thread. The diff highlighter reconstructs the old
and new file text by position rather than from @@ line ranges, so diffs that
arrive without real hunk headers still highlight.

Read content is normalized server-side: the cat -n line-number gutter some
providers emit is stripped so content is uniformly raw source, with the first
line number surfaced as offset for the client to rebuild the gutter.

packages/app/src/utils/tool-call-parsers.ts

@@ -1,4 +1,5 @@
 import { z } from "zod";
+import type { HighlightToken } from "@getpaseo/highlight";
 
 export interface DiffSegment {
   text: string;
@@ -9,6 +10,9 @@ export interface DiffLine {
   type: "add" | "remove" | "context" | "header";
   content: string;
   segments?: DiffSegment[];
+  // Syntax-highlight tokens for the code on this line (prefix char excluded),
+  // attached by highlightDiffLines when the file's language is supported.
+  tokens?: HighlightToken[];
 }
 
 function splitIntoLines(text: string): string[] {