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.

.gitignore

@@ -0,0 +1,36 @@
+# build output
+dist/
+# generated types
+.astro/
+
+# dependencies
+node_modules/
+
+# logs
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+
+# environment variables
+.env
+.env.production
+
+# macOS-specific files
+.DS_Store
+
+# jetbrains setting folder
+.idea/
+
+# superpowers brainstorming session artifacts
+.superpowers/
+
+# Obsidian workspace cache (per-machine, not for source control)
+src/world/.obsidian/workspace.json
+src/world/.obsidian/workspace-mobile.json
+src/world/.obsidian/workspace.json.bak
+src/world/.obsidian/cache
+docs/superpowers/specs/.obsidian/workspace.json
+docs/superpowers/specs/.obsidian/workspace-mobile.json
+docs/superpowers/specs/.obsidian/workspace.json.bak
+docs/superpowers/specs/.obsidian/cache