delete the landing app

Built and shipped from somewhere else now, so this copy was dead weight that still
carried its own third copy of the palette — `duck-teal` had three different definitions
across three apps, and this was one of them.

Removed: `src/apps/landing`, `scripts/build/landing.ts`, the `build:landing` script,
and the tree entry in CLAUDE.md.

`/landing-page-data` STAYS and is unrelated despite the name — it is the API the
sign-in screen asks whether registration is open. Worth saying because a grep for
"landing" hits both and only one of them was meant.

Nothing imported from the app. tsgo clean, frontend builds, the live app serves.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

package.json

@@ -17,7 +17,6 @@
     "prebuild": "bun run ./scripts/prebuild.ts",
     "build:web": "bun run ./scripts/build/web.ts",
     "build:dashboard": "bun run ./scripts/build/dashboard.ts",
-    "build:landing": "bun run ./scripts/build/landing.ts",
     "db:gen": "cd src/databases/officer_db && bun run generate",
     "db:push": "bun run scripts/gen-plugin-schemas.ts && cd src/databases/officer_db && bun run push",
     "db:migrate": "cd src/databases/officer_db && bun run migrate",