fix(chat): count a subagent's edits in the turn's Edited N files card (#86)

A skill that hands its work to subagents (vp-auto) showed "Edited 1 file"
for a turn that changed 4: a subagent's Write/Edit calls are in its own
agent-<id>.jsonl, so the card only saw the parent's.

- server/lib/agent-edits.js reads a subagent's transcript (readLines, a
  member's only as theirs) for the files it wrote or edited with their +/-
  lines, nested subagents folded in (3 levels), cached by size + mtime.
- The transcript route puts them on each Claude Agent/Task result as
  `edits`; the card adds them to the turn's own edits. A file only a
  subagent wrote is listed, never an artifact card (its versions are
  rebuilt from this transcript's inputs, which a subagent's are not).

client/src/lib/types.ts

@@ -3236,6 +3236,10 @@ export interface TranscriptContent {
   /** Present on a Write/Edit/MultiEdit "tool_result": the lines it added and
    *  removed (from Claude Code's `structuredPatch`). */
   diff?: { added: number; removed: number };
+  /** Present on an Agent/Task "tool_result" whose subagent (or one it started)
+   *  wrote or edited files: each file with its +/- lines (`counted`: the
+   *  results carried them). Read from the subagent's own transcript. */
+  edits?: { path: string; added: number; removed: number; counted: boolean }[];
   /** Present on an AskUserQuestion "tool_result": question text → the option
    *  the user picked, or what they typed. */
   answers?: Record<string, string>;