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.toml

@@ -11,7 +11,7 @@ members = [
 exclude = []
 
 [workspace.package]
-version = "0.1.1"
+version = "0.1.2"
 authors = ["Wickra Contributors"]
 edition = "2021"
 rust-version = "1.75"
@@ -23,7 +23,7 @@ keywords = ["finance", "trading", "indicators", "technical-analysis", "ta"]
 categories = ["finance", "mathematics", "science"]
 
 [workspace.dependencies]
-wickra-core = { path = "crates/wickra-core", version = "0.1.1" }
+wickra-core = { path = "crates/wickra-core", version = "0.1.2" }
 
 thiserror = "2"
 rayon = "1.10"