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

packages/hashline-core/tsconfig.json

@@ -0,0 +1,14 @@
+{
+  "compilerOptions": {
+    "target": "ESNext",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "lib": ["ESNext"],
+    "types": ["bun-types"]
+  },
+  "include": ["src/**/*"]
+}