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/file-text-canonicalization.ts

@@ -0,0 +1,40 @@
+export interface FileTextEnvelope {
+  content: string
+  hadBom: boolean
+  lineEnding: "\n" | "\r\n"
+}
+
+function detectLineEnding(content: string): "\n" | "\r\n" {
+  return content.includes("\r\n") ? "\r\n" : "\n"
+}
+
+function stripBom(content: string): { content: string; hadBom: boolean } {
+  if (!content.startsWith("\uFEFF")) {
+    return { content, hadBom: false }
+  }
+  return { content: content.slice(1), hadBom: true }
+}
+
+function normalizeToLf(content: string): string {
+  return content.replace(/\r\n/g, "\n").replace(/\r/g, "\n")
+}
+
+function restoreLineEndings(content: string, lineEnding: "\n" | "\r\n"): string {
+  if (lineEnding === "\n") return content
+  return content.replace(/\n/g, "\r\n")
+}
+
+export function canonicalizeFileText(content: string): FileTextEnvelope {
+  const stripped = stripBom(content)
+  return {
+    content: normalizeToLf(stripped.content),
+    hadBom: stripped.hadBom,
+    lineEnding: detectLineEnding(stripped.content),
+  }
+}
+
+export function restoreFileText(content: string, envelope: FileTextEnvelope): string {
+  const withLineEnding = restoreLineEndings(content, envelope.lineEnding)
+  if (!envelope.hadBom) return withLineEnding
+  return `\uFEFF${withLineEnding}`
+}