feat: add InputHalo landing page with DMG download flow

Add a marketing landing page for inputhalo.freno.me with a hero section
(theme-aware app icon, glitch title, tagline), feature highlights, and a
download section offering a macOS DMG via the tRPC signed-S3 URL endpoint
plus an App Store link.

Extract the download orchestration into a pure, side-effect-free helper
(query/performInputHaloDownload) so the asset-name and redirect contract is
unit-tested in isolation, mirroring the existing site-aware page-head /
nav-config split. Include dark and default app-icon exports in the public
folder.

src/routes/inputhalo/download.ts

@@ -0,0 +1,92 @@
+/**
+ * Pure, side-effect-free download orchestration for the InputHalo landing
+ * page (task 06).
+ *
+ * Extracted from the route component so the acceptance criterion —
+ * "download button calls `api.downloads.getDownloadUrl` with `'inputhalo'`
+ *  and redirects to the signed S3 URL" — can be unit-tested in `bun:test`
+ * without importing solid-js / `@solidjs/router` / `@solidjs/meta` (the same
+ * pattern established by `~/components/page-head-meta.ts` and
+ * `~/lib/nav-config.ts`).
+ *
+ * The route component (`./index.tsx`) is a thin wrapper that supplies the
+ * real `api` (the tRPC client) and a `redirect` that mutates
+ * `window.location.href`, plus loading/error UX. The data-flow contract
+ * lives here.
+ */
+
+/** tRPC asset name for the InputHalo macOS DMG (matches `downloads.tsx`). */
+export const INPUTHALO_ASSET_NAME = "inputhalo" as const;
+
+/** App Store listing for InputHalo (paid variant — "coming soon"). */
+export const INPUTHALO_APP_STORE_URL =
+  "https://apps.apple.com/us/app/inputhalo/" as const;
+
+/** Minimum macOS version supported by InputHalo (per Info.plist). */
+export const INPUTHALO_MIN_SYSTEM_VERSION = "14.6" as const;
+
+/** Public asset paths for the app icon, switched on dark/light theme. */
+export const INPUTHALO_ICON_DARK =
+  "/InputHalo Exports/InputHalo-iOS-Dark-1024x1024@1x.png" as const;
+export const INPUTHALO_ICON_DEFAULT =
+  "/InputHalo Exports/InputHalo-iOS-Default-1024x1024@1x.png" as const;
+
+/**
+ * Structural type of the slice of the tRPC client this helper consumes.
+ * Keeps the helper decoupled from the full `api` surface and testable with a
+ * stub.
+ */
+export interface DownloadQueryApi {
+  (input: { asset_name: string }): Promise<{ downloadURL: string }>;
+}
+
+/**
+ * Resolve the signed S3 download URL for the InputHalo DMG.
+ *
+ * Pure: issues the query via the supplied `api` callable and returns the
+ * resulting `downloadURL`. Throws if the underlying query rejects — the
+ * caller owns the user-facing error UX.
+ *
+ * @example
+ * ```ts
+ * const url = await queryInputHaloDownload(
+ *   (input) => api.downloads.getDownloadUrl.query(input)
+ * );
+ * ```
+ */
+export async function queryInputHaloDownload(
+  query: DownloadQueryApi
+): Promise<string> {
+  const data = await query({ asset_name: INPUTHALO_ASSET_NAME });
+  return data.downloadURL;
+}
+
+/**
+ * Drive the full DMG download flow: call the tRPC endpoint with the
+ * InputHalo asset name, then hand the signed URL to `redirect`.
+ *
+ * Returns a boolean indicating success so callers can branch their loading-
+ * state cleanup without a try/catch (errors are caught internally and surfaced
+ * via the `onError` callback — keeps the component body tidy).
+ *
+ * @param query    tRPC query callable (the `api.downloads.getDownloadUrl`
+ *                 bound method).
+ * @param redirect Side-effect invoked with the signed S3 URL (typically
+ *                 `(url) => { window.location.href = url; }`).
+ * @param onError  Optional error sink (defaults to `console.error`).
+ * @returns `true` on success, `false` if the query rejected.
+ */
+export async function performInputHaloDownload(
+  query: DownloadQueryApi,
+  redirect: (url: string) => void,
+  onError?: (error: unknown) => void
+): Promise<boolean> {
+  try {
+    const url = await queryInputHaloDownload(query);
+    redirect(url);
+    return true;
+  } catch (error) {
+    (onError ?? console.error)("InputHalo download error:", error);
+    return false;
+  }
+}