native: move Zig sources into packages/native (#1391)

Separate the native implementation from the TypeScript bindings. Keep
core on
the public bindings and keep the current native artifact packages and
release
workflows.

packages/native owns the Zig source, tests, benches, and vendor updates.
The
package is private and unpublished for now Core still packages the
@opentui/core-* artifacts. build:native, test:native, and bench:native
still
work from core and delegate to native.

Expose a Zig import root and a no-JS hello example for proof of concept,
not a focus point, just a smoke test.

bun.lock

@@ -92,6 +92,10 @@
         "solid-js",
       ],
     },
+    "packages/native": {
+      "name": "@opentui/native",
+      "version": "0.5.4",
+    },
     "packages/qrcode": {
       "name": "@opentui/qrcode",
       "version": "0.5.4",
@@ -560,6 +564,8 @@
 
     "@opentui/keymap": ["@opentui/keymap@workspace:packages/keymap"],
 
+    "@opentui/native": ["@opentui/native@workspace:packages/native"],
+
     "@opentui/qrcode": ["@opentui/qrcode@workspace:packages/qrcode"],
 
     "@opentui/react": ["@opentui/react@workspace:packages/react"],