chore: standalone Halfstreet repo scaffolding

- package.json: drop @astrojs/sitemap, fontsource fonts, wrangler,
  @cloudflare/workers-types, tsx, spotify scripts. Keep astro/yaml/zod
  + vitest/typescript/@astrojs/check/@types/node. Add GPL-3.0-or-later.
- astro.config.mjs: drop sitemap integration, sharp image config; set
  site to halfstreet.io.
- tsconfig.json: drop cloudflare-workers-types, drop functions/scripts
  from include.
- .gitignore: cloudflare-free; Obsidian workspace cache rules updated
  to post-rename src/world/.obsidian/ paths.
- README.md: stack, layout, design-doc index, license note.
- .woodpecker.yml: install + npm test + npm run build pipeline.

astro.config.mjs

@@ -0,0 +1,9 @@
+// @ts-check
+import { defineConfig } from 'astro/config'
+
+export default defineConfig({
+  site: 'https://halfstreet.io',
+  build: {
+    inlineStylesheets: 'auto',
+  },
+})