chore(node, readme): SPDX license, Node 18 engines, bench hardware spec (R15, R18, R19)

R15 — `bindings/node/package.json` and all six per-platform subpackage
templates (`npm/{darwin-arm64,darwin-x64,linux-arm64-gnu,linux-x64-gnu,
win32-arm64-msvc,win32-x64-msvc}/package.json`) plus the WASM
`release.yml` enrich step switch the `license` field from the npm
convention `SEE LICENSE IN LICENSE` to the SPDX identifier
`PolyForm-Noncommercial-1.0.0`. npm's license search and downstream
tooling can now surface the actual license.

R18 — every `engines.node` field is bumped from `>= 16` to `>= 18`.
The package's test script (`node --test __tests__/`) uses the built-in
`node --test` runner that landed in Node 18; advertising support for
Node 16 / 17 was a guarantee we never verified (CI tests on Node 18 /
20 only) and would have produced a confusing error on those versions.

R19 — README's benchmark section gains an explicit hardware /
software-version block and reframes the absolute µs values as a
relative-speedup snapshot rather than a universal contract. Also tells
the reader how to reproduce locally (`pip install -e
bindings/python[bench]` + `python -m benchmarks.compare_libraries`) and
where the CI artefact lives.

Side effects:

- R16 / R17 (built wheel under `bindings/python/dist/` and
  `examples/node/node_modules/`) — verified that both are already
  covered by `.gitignore` (`*.whl`, `dist/`, `**/node_modules/`) and
  were never tracked by git. The local directories have been cleared;
  no `.gitignore` change needed and no committed file removed.

bindings/node/npm/darwin-arm64/package.json

@@ -6,9 +6,9 @@
   "files": [
     "wickra.darwin-arm64.node"
   ],
-  "license": "SEE LICENSE IN LICENSE",
+  "license": "PolyForm-Noncommercial-1.0.0",
   "engines": {
-    "node": ">= 16"
+    "node": ">= 18"
   },
   "os": [
     "darwin"

bindings/node/npm/darwin-x64/package.json

@@ -6,9 +6,9 @@
   "files": [
     "wickra.darwin-x64.node"
   ],
-  "license": "SEE LICENSE IN LICENSE",
+  "license": "PolyForm-Noncommercial-1.0.0",
   "engines": {
-    "node": ">= 16"
+    "node": ">= 18"
   },
   "os": [
     "darwin"

bindings/node/npm/linux-arm64-gnu/package.json

@@ -6,9 +6,9 @@
   "files": [
     "wickra.linux-arm64-gnu.node"
   ],
-  "license": "SEE LICENSE IN LICENSE",
+  "license": "PolyForm-Noncommercial-1.0.0",
   "engines": {
-    "node": ">= 16"
+    "node": ">= 18"
   },
   "os": [
     "linux"

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

@@ -6,9 +6,9 @@
   "files": [
     "wickra.linux-x64-gnu.node"
   ],
-  "license": "SEE LICENSE IN LICENSE",
+  "license": "PolyForm-Noncommercial-1.0.0",
   "engines": {
-    "node": ">= 16"
+    "node": ">= 18"
   },
   "os": [
     "linux"

bindings/node/npm/win32-arm64-msvc/package.json

@@ -6,9 +6,9 @@
   "files": [
     "wickra.win32-arm64-msvc.node"
   ],
-  "license": "SEE LICENSE IN LICENSE",
+  "license": "PolyForm-Noncommercial-1.0.0",
   "engines": {
-    "node": ">= 16"
+    "node": ">= 18"
   },
   "os": [
     "win32"

bindings/node/npm/win32-x64-msvc/package.json

@@ -6,9 +6,9 @@
   "files": [
     "wickra.win32-x64-msvc.node"
   ],
-  "license": "SEE LICENSE IN LICENSE",
+  "license": "PolyForm-Noncommercial-1.0.0",
   "engines": {
-    "node": ">= 16"
+    "node": ">= 18"
   },
   "os": [
     "win32"

bindings/node/package.json

@@ -5,7 +5,7 @@
   "author": "kingchenc <kingchencp@gmail.com>",
   "main": "index.js",
   "types": "index.d.ts",
-  "license": "SEE LICENSE IN LICENSE",
+  "license": "PolyForm-Noncommercial-1.0.0",
   "keywords": [
     "trading",
     "indicators",
@@ -44,7 +44,7 @@
     }
   },
   "engines": {
-    "node": ">= 16"
+    "node": ">= 18"
   },
   "optionalDependencies": {
     "wickra-linux-x64-gnu": "0.1.4",