fix(web): skip empty Authorization header for forward-auth proxy compatibility

Centralize duplicated getToken() + Bearer header logic into a single
formatHeaders() helper in lib/api.ts. When no token exists, the
Authorization header is omitted entirely instead of sending an empty
Bearer token, which breaks forward-auth proxies like Authelia behind
Caddy.

Changes:
- Add formatHeaders() with try-catch around localStorage access
- Replace 20+ duplicated getToken() definitions across tool components
- Migrate all call sites including file-details, settings, change-password
- Update tests to verify header omission on empty token

Based on the fix proposed by @jules2689 in #6, with improvements:
file placement (lib/api.ts vs components), localStorage error handling,
simplified truthiness check, and complete call-site coverage.

Co-Authored-By: Julian Nadeau <julian@jnadeau.ca>

apps/web/src/components/tools/collage-settings.tsx

@@ -1,11 +1,8 @@
 import { Download, Loader2 } from "lucide-react";
 import { useState } from "react";
+import { formatHeaders } from "@/lib/api";
 import { useFileStore } from "@/stores/file-store";
 
-function getToken(): string {
-  return localStorage.getItem("stirling-token") || "";
-}
-
 type Layout = "2x2" | "3x3" | "1x3" | "2x1" | "3x1" | "1x2";
 
 const LAYOUTS: { value: Layout; label: string }[] = [
@@ -43,7 +40,7 @@ export function CollageSettings() {
 
       const res = await fetch("/api/v1/tools/collage", {
         method: "POST",
-        headers: { Authorization: `Bearer ${getToken()}` },
+        headers: formatHeaders(),
         body: formData,
       });