🔧 Declare Node 26 as the supported runtime

- Add .node-version (single line: '26') so fnm/nvm/volta/mise and the
  VS Code Node version manager extension auto-switch when entering the
  project directory
- engines.node in package.json: bump from '>=22.6' to '>=26' (npm-side
  install-time declaration)
- Drop --experimental-strip-types flag from node --test invocations:
  Node 26 has --strip-types unflagged
- .github/workflows/ci.yml: switch from hard-coded node-version: 24 to
  node-version-file: .node-version in both build and publish jobs so CI
  follows the .node-version file (single source of truth)
- .npmignore: add .node-version (developer-tool file, not for publish)
- .vscode/settings.json: pin js/ts.tsdk.path to node_modules/typescript/lib
  so the editor uses the project's TS 7, not a different global install
- .vscode/extensions.json: swap ms-vscode.vscode-typescript-next for
  typescriptteam.native-preview (the official TS team extension that
  ships nightly TS support, including TS 7)
- cspell: add 'esbenp' and 'typescriptteam' to dictionary
- package-lock.json: regenerated for engines.node >=26

tsconfig.json target/lib are unchanged: es2024 is the highest stable ES
target TS 7.0.2 ships, and Node 26 supports all ES2024 features natively.

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
             - uses: actions/checkout@v4
             - uses: actions/setup-node@v4
               with:
-                  node-version: 24
+                  node-version-file: .node-version
                   cache: "npm"
             - run: npm ci
             - run: npm run build
@@ -34,7 +34,7 @@ jobs:
             - uses: actions/checkout@v4
             - uses: actions/setup-node@v4
               with:
-                  node-version: 24
+                  node-version-file: .node-version
                   registry-url: "https://registry.npmjs.org/"
             - run: npm ci
             - run: npm run build