fix(node): commit npm/<platform>/ templates + optionalDependencies

`napi create-npm-dir` failed in CI with both invocations we tried:
positional arg form (`-t <triple> .`) was rejected as extraneous,
and the no-arg form crashed with "path must be a string, received
undefined". The fix used by every napi-rs reference project: commit
the four platform package.json templates directly under
bindings/node/npm/<target>/ instead of generating them at publish time.

- bindings/node/npm/{linux-x64-gnu,darwin-x64,darwin-arm64,win32-x64-msvc}/
  each contain a static package.json with the correct os / cpu / libc
  filters so npm only installs the right binary per platform.
- Main package.json gains optionalDependencies referencing all four
  platform packages by version, so `npm install wickra` pulls the
  matching binary on each user's machine.
- Release workflow drops the broken `create-npm-dir` loop. The
  `napi artifacts` step now just copies the .node files from the
  build artefacts into the existing npm/ directories before publish.

Bump every version to 0.1.2; cargo / pypi / wickra-wasm jobs are
idempotent so they accept the 0.1.1 they already published while still
emitting the new 0.1.2.

bindings/node/npm/linux-x64-gnu/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "wickra-linux-x64-gnu",
+  "version": "0.1.2",
+  "description": "Native binding for wickra (linux x64 GNU). Installed automatically as an optional dependency of wickra on matching platforms.",
+  "main": "wickra.linux-x64-gnu.node",
+  "files": [
+    "wickra.linux-x64-gnu.node"
+  ],
+  "license": "SEE LICENSE IN LICENSE",
+  "engines": {
+    "node": ">= 16"
+  },
+  "os": [
+    "linux"
+  ],
+  "cpu": [
+    "x64"
+  ],
+  "libc": [
+    "glibc"
+  ],
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/kingchenc/wickra"
+  },
+  "homepage": "https://github.com/kingchenc/wickra"
+}