docs: add installation instructions for Forgejo registry and update package.json for publishing

.forgejo/workflows/publish-forgejo-npm.yml

@@ -0,0 +1,36 @@
+name: Publish to Forgejo npm Registry
+
+on:
+  push:
+    tags:
+      - "v*"
+  workflow_dispatch:
+
+jobs:
+  publish:
+    runs-on: native
+    env:
+      NODE_AUTH_TOKEN: ${{ secrets.FORGEJO_NPM_TOKEN }}
+      REGISTRY_URL: https://git.mizuki.guru/api/packages/imnyang/npm/
+      SCOPE: imnyang
+    steps:
+      - name: Checkout
+        uses: https://code.forgejo.org/actions/checkout@v4
+
+      - name: Configure npm auth for Forgejo registry
+        run: |
+          REGISTRY_HOST="${REGISTRY_URL#https://}"
+          REGISTRY_HOST="${REGISTRY_HOST#http://}"
+          {
+            echo "@${SCOPE}:registry=${REGISTRY_URL}"
+            echo "//${REGISTRY_HOST}:_authToken=${NODE_AUTH_TOKEN}"
+            echo "always-auth=true"
+          } > "$HOME/.npmrc"
+
+      - name: Install, build, and publish in Nix shell
+        run: |
+          nix shell nixpkgs#nodejs_24 nixpkgs#pnpm -c sh -lc '
+            pnpm install --frozen-lockfile
+            pnpm build
+            pnpm publish --no-git-checks --registry "$REGISTRY_URL"
+          '