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.

README.md

@@ -0,0 +1,42 @@
+# Halfstreet
+
+A gothic text adventure. Second person, present tense, sparse — never explains.
+
+Style anchors: Le Fanu's *Carmilla*, Shirley Jackson's *The Haunting of Hill House*, M.R. James's ghost stories.
+
+Played at [halfstreet.io](https://halfstreet.io).
+
+## Stack
+
+- [Astro](https://astro.build) static site
+- TypeScript engine — pure (no DOM, `Date`, `Math.random`, or console)
+- World content authored in markdown (rooms, items, encounters, endings) under `src/world/`
+- [Vitest](https://vitest.dev) for tests
+
+## Development
+
+```sh
+npm install
+npm test          # engine + world tests
+npm run dev       # local dev server
+npm run build     # type-check + production build
+```
+
+## Layout
+
+- `src/engine/` — parser, dispatcher, encounter logic
+- `src/ui/` — terminal renderer, theme, chips
+- `src/world/` — markdown content (rooms, items, encounters, endings)
+- `src/pages/index.astro` — entry page
+
+## Design docs
+
+- `docs/superpowers/specs/halfstreet-bible.md` — content bible (canonical world)
+- `docs/superpowers/specs/2026-05-08-mystery-text-adventure-design.md` — engine/UI architecture
+- `docs/superpowers/specs/halfstreet-followon-notes.md` — pending engine work before authoring more rooms
+- `docs/superpowers/specs/2026-05-09-mystery-markdown-migration-design.md` — markdown content migration design
+- `docs/superpowers/plans/2026-05-09-mystery-markdown-migration.md` — migration plan that was executed
+
+## License
+
+GPL-3.0-or-later. See [`LICENSE`](LICENSE).