chore: add VS Code workspace config and improve CI infrastructure

Add .vscode/ with Biome formatter, Tailwind, Vitest, Playwright, and
Python debug configs. Extract shared pnpm/Node setup into a composite
GitHub Action and add Dependabot and dependency-review workflows.

.github/workflows/deploy-docs.yml

@@ -17,15 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-
-      - uses: pnpm/action-setup@v4
-
-      - uses: actions/setup-node@v4
-        with:
-          node-version: 22
-          cache: pnpm
-
-      - run: pnpm install --frozen-lockfile
+      - uses: ./.github/actions/setup
 
       - name: Build Docs
         run: pnpm --filter @snapotter/docs docs:build