Restructure into pnpm monorepo with game shell, docs, and SpacetimeDB backend

- Restructure flat static prototype into pnpm workspace monorepo
- apps/game: playable shell with R3F 3D scene, HUD, SpacetimeDB connection
- apps/docs: design docs and prototypes
- apps/site: landing page
- packages/ui: shared Button and Panel primitives
- services/spacetimedb: backend module (9 tables, 11 reducers)
- Archive legacy static files to archive/legacy-static/
- Game loop: connect, undock, target, approach, dock, mine, sell
- Add pnpm-workspace.yaml, tsconfig.base.json, spacetime.json

packages/ui/src/primitives/Button.tsx

@@ -0,0 +1,55 @@
+import type { ButtonHTMLAttributes, AnchorHTMLAttributes, ReactNode } from "react";
+
+type ButtonTone = "primary" | "secondary" | "ghost";
+
+type BaseProps = {
+  children: ReactNode;
+  className?: string;
+  tone?: ButtonTone;
+};
+
+type NativeButtonProps = BaseProps &
+  ButtonHTMLAttributes<HTMLButtonElement> & {
+    href?: never;
+  };
+
+type AnchorButtonProps = BaseProps &
+  AnchorHTMLAttributes<HTMLAnchorElement> & {
+    href: string;
+  };
+
+export type ButtonProps = NativeButtonProps | AnchorButtonProps;
+
+const tones: Record<ButtonTone, string> = {
+  primary: "border-accent bg-accent text-bg hover:bg-accent-hover",
+  secondary: "border-border bg-surface-raised text-fg hover:border-border-light hover:bg-surface-hover",
+  ghost: "border-transparent bg-transparent text-cyan hover:border-border-light hover:bg-surface",
+};
+
+export function Button({ children, className = "", tone = "secondary", ...props }: ButtonProps) {
+  const classes = [
+    "inline-flex min-h-10 cursor-pointer items-center justify-center gap-2 rounded-md border px-4 py-2 text-sm font-semibold transition-colors duration-150 disabled:cursor-not-allowed disabled:opacity-55",
+    tones[tone],
+    className,
+  ]
+    .filter(Boolean)
+    .join(" ");
+
+  if ("href" in props) {
+    const anchorProps = props as Omit<AnchorButtonProps, keyof BaseProps>;
+
+    return (
+      <a className={classes} {...anchorProps}>
+        {children}
+      </a>
+    );
+  }
+
+  const buttonProps = props as Omit<NativeButtonProps, keyof BaseProps>;
+
+  return (
+    <button className={classes} {...buttonProps}>
+      {children}
+    </button>
+  );
+}