perf(hooks,tools): optimize string operations and reduce redundant iterations

- output-renderer, hashline-edit-diff: replace str += with array join (H2)
- auto-slash-command: single-pass Map grouping instead of 6x filter (M1)
- comment-checker: hoist Zod schema to module scope (M2)
- session-last-agent: reverse iterate sorted array instead of sort+reverse (L2)

src/tools/hashline-edit/hashline-edit-diff.ts

@@ -4,7 +4,7 @@ export function generateHashlineDiff(oldContent: string, newContent: string, fil
   const oldLines = oldContent.split("\n")
   const newLines = newContent.split("\n")
 
-  let diff = `--- ${filePath}\n+++ ${filePath}\n`
+  const parts: string[] = [`--- ${filePath}\n+++ ${filePath}\n`]
   const maxLines = Math.max(oldLines.length, newLines.length)
 
   for (let i = 0; i < maxLines; i += 1) {
@@ -14,18 +14,18 @@ export function generateHashlineDiff(oldContent: string, newContent: string, fil
     const hash = computeLineHash(lineNum, newLine)
 
     if (i >= oldLines.length) {
-      diff += `+ ${lineNum}#${hash}|${newLine}\n`
+      parts.push(`+ ${lineNum}#${hash}|${newLine}\n`)
       continue
     }
     if (i >= newLines.length) {
-      diff += `- ${lineNum}#  |${oldLine}\n`
+      parts.push(`- ${lineNum}#  |${oldLine}\n`)
       continue
     }
     if (oldLine !== newLine) {
-      diff += `- ${lineNum}#  |${oldLine}\n`
-      diff += `+ ${lineNum}#${hash}|${newLine}\n`
+      parts.push(`- ${lineNum}#  |${oldLine}\n`)
+      parts.push(`+ ${lineNum}#${hash}|${newLine}\n`)
     }
   }
 
-  return diff
+  return parts.join("")
 }