feat(hashline-edit): add autocorrect, BOM/CRLF normalization, and file creation support

Implements key features from oh-my-pi to improve agent editing success rates:

- Autocorrect v1: single-line merge expansion, wrapped line restoration,
  paired indent restoration (autocorrect-replacement-lines.ts)
- BOM/CRLF normalization: canonicalize on read, restore on write
  (file-text-canonicalization.ts)
- Pre-validate all hashes before mutation (edit-ordering.ts)
- File creation via append/prepend operations (new types + executor logic)
- Modular refactoring: split edit-operations.ts into focused modules
  (primitives, ordering, deduplication, diff, executor)
- Enhanced tool description with operation choice guide and recovery hints

All 50 tests pass. TypeScript clean. Build successful.

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

@@ -0,0 +1,31 @@
+import { computeLineHash } from "./hash-computation"
+
+export function generateHashlineDiff(oldContent: string, newContent: string, filePath: string): string {
+  const oldLines = oldContent.split("\n")
+  const newLines = newContent.split("\n")
+
+  let diff = `--- ${filePath}\n+++ ${filePath}\n`
+  const maxLines = Math.max(oldLines.length, newLines.length)
+
+  for (let i = 0; i < maxLines; i += 1) {
+    const oldLine = oldLines[i] ?? ""
+    const newLine = newLines[i] ?? ""
+    const lineNum = i + 1
+    const hash = computeLineHash(lineNum, newLine)
+
+    if (i >= oldLines.length) {
+      diff += `+ ${lineNum}#${hash}:${newLine}\n`
+      continue
+    }
+    if (i >= newLines.length) {
+      diff += `- ${lineNum}#  :${oldLine}\n`
+      continue
+    }
+    if (oldLine !== newLine) {
+      diff += `- ${lineNum}#  :${oldLine}\n`
+      diff += `+ ${lineNum}#${hash}:${newLine}\n`
+    }
+  }
+
+  return diff
+}