feat(web): hold a Screen Wake Lock while reading or listening

New wake-lock.ts engine (sanctioned island, dependency-injected for
tests): feature-detected navigator.wakeLock, silent no-op when
unsupported or denied, and the spec-mandated force-release-on-hide →
re-acquire-on-visible loop handled via the sentinel release event.
The player acquires on play and releases on pause (sleep-timer fades
ride the same path); the reader holds the lock for the session. Both
gate on the keep_screen_awake preference — data-keep-awake on the
player root, keepScreenAwake in readerInitExpr.

Hidden-tab playback intentionally does not keep the screen awake:
the spec forbids screen wake locks for hidden documents.

web/src/reader/reader.ts

@@ -7,6 +7,7 @@ import { getToken } from "../storage";
 import { showToast } from "../toast";
 import { renderNoteHtml, richPasteToMarkdown } from "../markdown";
 import { extractPdfPages, searchPdfPages, type PdfPageText } from "./pdf-search";
+import { WakeLockManager } from "../wake-lock";
 
 const HIGHLIGHT_COLORS = ["#ffd54f", "#a5d6a7", "#90caf9", "#f48fb1", "#ce93d8"];
 
@@ -398,6 +399,10 @@ document.addEventListener("alpine:init", () => {
     // comic reader treatment — bookmarks only, no text-selection
     // highlights, no in-book search.
     treatAsComic: false as boolean,
+    // Screen wake lock (keep_screen_awake profile preference): held for
+    // the whole reading session; the browser force-releases it when the
+    // page hides and the manager re-acquires on visibility regain.
+    wakeLock: new WakeLockManager(),
     comicFlow: "paged" as string,
     fxBrightness: 1 as number,
     fxContrast: 1 as number,
@@ -627,9 +632,13 @@ document.addEventListener("alpine:init", () => {
       readingDirection: string;
       mangaType: string;
       treatAsComic: boolean;
+      keepScreenAwake: boolean;
     }) {
       this.mediaItemId = config.mediaItemId;
       this.treatAsComic = config.treatAsComic;
+      // Hold the display awake for the reading session (best-effort;
+      // unsupported browsers and power-saver denials are silent no-ops).
+      if (config.keepScreenAwake) void this.wakeLock.acquire();
       // Reading state (position, bookmarks, annotations) is never baked
       // into the rendered page: the web reader is intrinsically tied to
       // the server, so it reads all of it from the APIs at open time —