refactor: reduce cyclomatic complexity of settings, tool data and layout sanitizers

Add characterization tests first, then split the hot spots into small helpers:
- STT/TTS settings updates move to extensions/piagentui-speech-settings.ts (rule tables)
- defaultExtractData is split into diff/diagnostic/output extractors
- getToolSummaryCategory becomes an ordered rule table (toolSummary.ts)
- sanitizePersistedTerminalLayoutMap is split per level
- duplicated diff stats helpers are merged into utils/diffStats.ts

src/features/message/parts/ToolPartView.tsx

@@ -1,6 +1,6 @@
 import { memo, useEffect, useMemo, useRef, useState } from 'react'
 import { useTranslation } from 'react-i18next'
-import { diffLines } from 'diff'
+import { computeDiffStats } from '../../../utils/diffStats'
 import { ChevronDownIcon, ChevronRightIcon } from '../../../components/Icons'
 import type { ToolPart } from '../../../types/message'
 import { useDelayedRender } from '../../../hooks'
@@ -203,7 +203,7 @@ export const ToolPartView = memo(function ToolPartView({
   if (descriptive) {
     const hasDiffFiles = !!toolData.files?.length
     // diffStats 可能从 metadata 来，也可能需要从 diff 数据计算
-    const diffStats = toolData.diffStats || computeDiffStatsFromData(toolData)
+    const diffStats = toolData.diffStats || computeDiffStats(toolData)
 
     return (
       <div className="group py-0.5">
@@ -451,47 +451,6 @@ function isReadableTool(toolName: string): boolean {
   return READABLE_TOOL_PATTERNS.test(toolName.toLowerCase())
 }
 
-/** 从 diff 数据计算 diffStats（当 metadata 没给 diffStats 时用） */
-function computeDiffStatsFromData(data: {
-  diff?: { before: string; after: string } | string
-  files?: Array<{ before?: string; after?: string; additions?: number; deletions?: number }>
-}): { additions: number; deletions: number } | undefined {
-  // 多文件
-  if (data.files?.length) {
-    let additions = 0,
-      deletions = 0
-    for (const f of data.files) {
-      if (f.additions !== undefined) additions += f.additions
-      if (f.deletions !== undefined) deletions += f.deletions
-      if (f.additions === undefined && f.before !== undefined && f.after !== undefined) {
-        const s = computeDiffPair(f.before, f.after)
-        additions += s.additions
-        deletions += s.deletions
-      }
-    }
-    return additions || deletions ? { additions, deletions } : undefined
-  }
-
-  // 单个 diff
-  if (data.diff && typeof data.diff === 'object') {
-    const s = computeDiffPair(data.diff.before, data.diff.after)
-    return s.additions || s.deletions ? s : undefined
-  }
-
-  return undefined
-}
-
-function computeDiffPair(before: string, after: string): { additions: number; deletions: number } {
-  const changes = diffLines(before, after)
-  let additions = 0,
-    deletions = 0
-  for (const c of changes) {
-    if (c.added) additions += c.count || 0
-    if (c.removed) deletions += c.count || 0
-  }
-  return { additions, deletions }
-}
-
 // ============================================
 // ToolBody - 根据工具类型选择渲染器
 // ============================================