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/constants.ts

@@ -1,10 +1,6 @@
-export const NIBBLE_STR = "ZPMQVRWSNKTXJBYH"
-
-export const HASHLINE_DICT = Array.from({ length: 256 }, (_, i) => {
-  const high = i >>> 4
-  const low = i & 0x0f
-  return `${NIBBLE_STR[high]}${NIBBLE_STR[low]}`
-})
-
-export const HASHLINE_REF_PATTERN = /^([0-9]+)#([ZPMQVRWSNKTXJBYH]{2})$/
-export const HASHLINE_OUTPUT_PATTERN = /^([0-9]+)#([ZPMQVRWSNKTXJBYH]{2})\|(.*)$/
+export {
+  NIBBLE_STR,
+  HASHLINE_DICT,
+  HASHLINE_REF_PATTERN,
+  HASHLINE_OUTPUT_PATTERN,
+} from "@oh-my-opencode/hashline-core"