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.

Cargo.lock

@@ -1883,7 +1883,7 @@ dependencies = [
 
 [[package]]
 name = "wickra"
-version = "0.1.1"
+version = "0.1.2"
 dependencies = [
  "approx",
  "criterion",
@@ -1894,7 +1894,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-core"
-version = "0.1.1"
+version = "0.1.2"
 dependencies = [
  "approx",
  "proptest",
@@ -1904,7 +1904,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-data"
-version = "0.1.1"
+version = "0.1.2"
 dependencies = [
  "approx",
  "csv",
@@ -1922,7 +1922,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-node"
-version = "0.1.1"
+version = "0.1.2"
 dependencies = [
  "napi",
  "napi-build",
@@ -1932,7 +1932,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-python"
-version = "0.1.1"
+version = "0.1.2"
 dependencies = [
  "numpy",
  "pyo3",
@@ -1941,7 +1941,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-wasm"
-version = "0.1.1"
+version = "0.1.2"
 dependencies = [
  "console_error_panic_hook",
  "js-sys",