refactor(packages): extract hashline-core package

Move the hash-anchored edit core (hash computation, validation, edit operations, text normalization, chunk formatter, diff utilities, and a runtime-aware xxHash32 binding) into a new @oh-my-opencode/hashline-core workspace package.

The src/tools/hashline-edit/ surface becomes a set of thin re-export shims, so existing import paths in the plugin keep working while the pure logic lives behind a stable package boundary that has no opencode runtime dependencies.

Tests: bun test packages/hashline-core src/tools/hashline-edit

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

@@ -1,31 +1 @@
-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")
-
-  const parts: string[] = [`--- ${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) {
-      parts.push(`+ ${lineNum}#${hash}|${newLine}\n`)
-      continue
-    }
-    if (i >= newLines.length) {
-      parts.push(`- ${lineNum}#  |${oldLine}\n`)
-      continue
-    }
-    if (oldLine !== newLine) {
-      parts.push(`- ${lineNum}#  |${oldLine}\n`)
-      parts.push(`+ ${lineNum}#${hash}|${newLine}\n`)
-    }
-  }
-
-  return parts.join("")
-}
+export { generateHashlineDiff } from "@oh-my-opencode/hashline-core"