chore: drop unused assets, primitives and dead functions

The Next.js starter left five SVGs in public/ that nothing references.
Eight shadcn primitives were vendored in but rendered nowhere: avatar,
form, popover, progress, separator, sheet, table and tooltip. Removing
them frees five Radix packages plus react-hook-form, its resolvers and
zod, none of which the app had wired up.

getAccumulatedScoreMessage was imported by GameClient and never called.
getRandomCityLocationFromBbox had no caller at all, so it goes with its
tests rather than leaving coverage pointed at unreachable code.

The docs claimed a form and validation stack the project never used, and
listed components that are no longer vendored.

docs/tech-stack.md

@@ -35,10 +35,10 @@
 - **class-variance-authority**: Component variant management
 - **tailwind-merge + clsx**: Dynamic class name handling
 
-## Form Handling & Validation
-- **react-hook-form**: Form state management
-- **@hookform/resolvers**: Form validation resolvers
-- **zod**: Schema validation
+## Testing
+- **Vitest**: Test runner for the logic in `src/lib/`
+- **In-memory Upstash fake**: Default backing store, no service required
+- **SRH + Redis (Docker)**: Optional lane running the same tests against real Redis
 
 ## Development & Analytics
 - **ESLint**: Code linting with Next.js configuration