Restructure shared Astro sources and import aliases (#2737)

shared/lib/include-args.ts

@@ -0,0 +1,11 @@
+/**
+ * Reproduces the LiquidJS `include['x']` meta-property bug: when a param isn't
+ * explicitly passed, referencing it as a bare property (rather than a lookup)
+ * falls back to the include's argument COUNT instead of undefined. Some ported
+ * components (ui/spinner.html, ui/nav-segmented.html) rely on this to emit
+ * "junk" classes like `spinner-border-2` / `nav-2` that the DOM parity diff
+ * does not strip, so they must be reproduced verbatim.
+ */
+export function includeArgCount(props: Record<string, unknown>, keys: readonly string[]): number {
+  return keys.filter((k) => props[k] !== undefined).length
+}