fix: root page 500 — resolve home.html for dev & prod layouts

handleHome looked up `${import.meta.dir}/home.html` which exists in neither
layout: dev (src/interfaces/http/controllers/) nor prod bundle
($out/share/teleuploader/dist/ — flake copies home.html beside dist/).

Add resolveHomeHtml(): walk up from import.meta.dir (bounded) to find
home.html. Works for dev (src/home.html, 4 levels up) and prod
(../home.html, 1 level up). Fails fast with a clear error instead of a
bare ENOENT 500. Tests cover both layouts + not-found fallback.

src/interfaces/http/controllers/home-controller.ts

@@ -1,15 +1,60 @@
+import { existsSync } from 'node:fs';
+import { dirname, join } from 'node:path';
 import type { BunFile } from 'bun';
 
+/**
+ * Maximum number of parent directories to walk up when locating home.html.
+ * Deep enough for the dev layout (controllers/ -> src/ = 4 levels) with margin.
+ */
+const MAX_PARENT_WALK = 6;
+
+/**
+ * Resolves the absolute path to `home.html` by walking up from `startDir`.
+ *
+ * The file lives at different depths depending on how the app is run:
+ * - Dev (`bun --hot src/index.ts`): `import.meta.dir` is
+ *   `src/interfaces/http/controllers/`, home.html lives at `src/home.html`
+ *   (4 levels up).
+ * - Prod (bundled `dist/index.js`): `import.meta.dir` is
+ *   `$out/share/teleuploader/dist/`, home.html lives next to dist/
+ *   (1 level up, per flake.nix installPhase).
+ *
+ * Returns the first existing candidate, or `null` if none is found within
+ * the walk bound.
+ *
+ * @param startDir - Directory to start the search from (typically `import.meta.dir`).
+ * @param maxDepth - Maximum number of parent directories to walk (default: 6).
+ * @returns Absolute path to home.html, or `null` if not found.
+ */
+export const resolveHomeHtml = (startDir: string, maxDepth = MAX_PARENT_WALK): string | null => {
+  let dir = startDir;
+  for (let depth = 0; depth <= maxDepth; depth++) {
+    const candidate = join(dir, 'home.html');
+    if (existsSync(candidate)) return candidate;
+    const parent = dirname(dir);
+    if (parent === dir) break;
+    dir = parent;
+  }
+  return null;
+};
+
 /**
  * Handles the home/dashboard page request.
  *
- * Reads the `home.html` file from the adjacent directory and serves it as
- * an HTML response with UTF-8 charset.
+ * Reads the `home.html` file and serves it as an HTML response with UTF-8
+ * charset. Fails fast with a clear error when the file cannot be located
+ * instead of letting Bun.serve swallow the ENOENT into a bare 500.
  *
  * @returns An HTML response containing the home page content.
  */
 export const handleHome = async (): Promise<Response> => {
-  const html = await (Bun.file(`${import.meta.dir}/home.html`) as BunFile).text();
+  const homeHtml = resolveHomeHtml(import.meta.dir);
+  if (!homeHtml) {
+    throw new Error(
+      `home.html not found — looked up from ${import.meta.dir} and ${MAX_PARENT_WALK} parent dirs`,
+    );
+  }
+  const html = await (Bun.file(homeHtml) as BunFile).text();
   return new Response(html, {
     status: 200,
     headers: {