fix(ui): cookie-authed users' writes silently stranded behind bearer gates

THE CLASS: the /api JWT middleware's TokenLookup is
"cookie:token,header:Authorization:Bearer" — the token cookie always
rides same-origin fetches, so a signed-in user never needs the
localStorage bearer. But a dozen call sites gated their fetch on
`localStorage.getItem("token")` and early-returned when absent. The
global 401 interceptor CLEARS that localStorage entry on any session
rotation/blip — after which every gated write silently did nothing:
theme changes reverted on reload (the reported "can no longer change
themes", on top of the interpolation bug d5dbaa48 fixed), chain-order
selects, collection deletion, Add-to-collection submits, filter
save/load/delete, conflict actions, linking actions, stats charts,
tag suggestions, device management, admin scanner actions — all dead
for perfectly authenticated cookie users.

Fix: storage.ts exports authHeaders() (bearer when present, cookie
carries otherwise) and every gate/header site now uses it — theme.ts,
collections.ts (htmx auth, doRemoveBook/doBulkRemove, setChainOrder),
bookPicker submit, filter_builder suggestions + match count,
collection-rules apply hook, bookshelf save/load/delete filter,
conflicts x4, linking x3, admin scanner actions + polls (requireToken
removed — its "Session expired" toast fired for cookie users too),
dashboard preferences/sections, custom-section-builder, header
scanner poll, stats x3, tag suggestions, profile delete-account
(which also wrongly redirected cookie users to /login), and
device-management x4. Reads keep their graceful-empty behavior; the
bearers still ride along when present.

Pinned: the knob-matrix theme spec now REMOVES localStorage.token and
asserts the theme PUT still fires (cookie-only) and the class flips —
the exact strand that started this.

Found by noticing the panel browser's Nord click switched the class
but produced no PUT: the persistence half was gated on a token the
401 interceptor had cleared.

web/src/dashboard.ts

@@ -1,4 +1,5 @@
 import { Alpine } from "./alpine";
+import { authHeaders } from "./storage";
 import { apiPost, apiPut } from "./api";
 import { showToast } from "./toast";
 import { initLibrarySwitcher, switchWithTransition } from "./library-switcher";
@@ -22,7 +23,7 @@ async function openDashboardSettings(): Promise<void> {
   // scope — the server returns that row when library_id is absent.
   const query = libraryId ? `?library_id=${encodeURIComponent(libraryId)}` : "";
   const response = await fetch(`/api/dashboard/preferences${query}`, {
-    headers: { Authorization: `Bearer ${localStorage.getItem("token")}` },
+    headers: authHeaders(),
   });
 
   if (response.ok) {
@@ -89,7 +90,7 @@ async function fetchAndRenderSections(libraryId: string): Promise<void> {
   const param = libraryId ? `library_id=${libraryId}` : "";
   const response = await fetch(`/api/dashboard/sections?${param}`, {
     headers: {
-      Authorization: `Bearer ${localStorage.getItem("token")}`,
+      ...authHeaders(),
       "Content-Type": "application/json",
     },
   });
@@ -535,7 +536,7 @@ function initDashboard() {
         const param = libraryId ? `library_id=${libraryId}` : "";
         const response = await fetch(`/api/dashboard/sections?${param}`, {
           headers: {
-            Authorization: `Bearer ${localStorage.getItem("token")}`,
+            ...authHeaders(),
             "Content-Type": "application/json",
           },
         });