feat(web): unified reader with reading settings, faster lists, a11y

- New Reader (desktop + mobile): loads full content on open, prefetches
  the next article, reading progress and time, "Aa" settings (light /
  sepia / dark / auto theme, serif / sans / Atkinson Hyperlegible font,
  size, line height, measure), Space-to-next, keyboard shortcuts, focus
  management, inert background, URL-driven (?a=) so Back closes it.
- Dashboard: cursor pagination, unread/all filter, CSS grid (no masonry),
  no re-sorting under the reader, optimistic cache patches instead of
  refetch storms, "new articles" banner, error/offline states, j/k/o/m/s/v
  shortcuts and help dialog.
- Cards: keyboard-openable, lazy <img>, memoized, touch-only swipe.
- Focus mode: framer drag (drop @use-gesture), Read button, undo restores
  unread state, arrow keys.
- WebSocket: single connection, backoff, cache patching, no console logs.
- Contrast fixes (on-nature tokens), 44px targets, lang="fr", reduced
  motion, self-hosted fonts, theme applied before first paint.
- Code splitting + vendor chunk, prompt-based PWA updates, smaller
  precache, offline cache for opened articles and images, caches cleared
  on logout; upgrade react-router (CVE), drop unused deps and assets.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/stores/prefsStore.ts

@@ -0,0 +1,90 @@
+import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
+
+export type ThemePref = 'system' | 'light' | 'sepia' | 'dark';
+export type ReaderFont = 'serif' | 'sans' | 'legible';
+export type ReaderWidth = 'narrow' | 'medium' | 'wide';
+
+interface PrefsState {
+    theme: ThemePref;
+    /** Article body font size in px. */
+    fontSize: number;
+    lineHeight: number;
+    width: ReaderWidth;
+    font: ReaderFont;
+    /** Dashboard filter: show only unread articles. */
+    unreadOnly: boolean;
+    setTheme: (t: ThemePref) => void;
+    setFontSize: (n: number) => void;
+    setLineHeight: (n: number) => void;
+    setWidth: (w: ReaderWidth) => void;
+    setFont: (f: ReaderFont) => void;
+    setUnreadOnly: (v: boolean) => void;
+    resetReader: () => void;
+}
+
+// Research-backed defaults: ~65ch measure, 19px body, 1.65 line-height.
+const READER_DEFAULTS = { fontSize: 19, lineHeight: 1.65, width: 'medium' as ReaderWidth, font: 'serif' as ReaderFont };
+
+export const FONT_SIZE_MIN = 15;
+export const FONT_SIZE_MAX = 26;
+
+const THEME_COLORS: Record<Exclude<ThemePref, 'system'>, string> = {
+    light: '#F7F4EC',
+    sepia: '#F4ECD8',
+    dark: '#121612',
+};
+
+function resolveTheme(pref: ThemePref): Exclude<ThemePref, 'system'> {
+    if (pref !== 'system') return pref;
+    return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
+}
+
+/** Applies the theme classes on <html>; mirrored by public/theme-init.js to avoid a flash on load. */
+export function applyTheme(pref: ThemePref) {
+    const theme = resolveTheme(pref);
+    const root = document.documentElement;
+    root.classList.toggle('dark', theme === 'dark');
+    root.classList.toggle('sepia', theme === 'sepia');
+    root.style.colorScheme = theme === 'dark' ? 'dark' : 'light';
+    document.querySelector('meta[name="theme-color"]')?.setAttribute('content', THEME_COLORS[theme]);
+    try {
+        if (pref === 'system') localStorage.removeItem('theme');
+        else localStorage.setItem('theme', pref);
+    } catch {
+        /* storage unavailable (private mode) */
+    }
+}
+
+export const usePrefs = create<PrefsState>()(
+    persist(
+        (set) => ({
+            theme: 'system',
+            ...READER_DEFAULTS,
+            unreadOnly: true,
+            setTheme: (theme) => {
+                applyTheme(theme);
+                set({ theme });
+            },
+            setFontSize: (fontSize) => set({ fontSize: Math.min(FONT_SIZE_MAX, Math.max(FONT_SIZE_MIN, fontSize)) }),
+            setLineHeight: (lineHeight) => set({ lineHeight }),
+            setWidth: (width) => set({ width }),
+            setFont: (font) => set({ font }),
+            setUnreadOnly: (unreadOnly) => set({ unreadOnly }),
+            resetReader: () => set(READER_DEFAULTS),
+        }),
+        {
+            name: 'flowreader-prefs',
+            onRehydrateStorage: () => (state) => {
+                if (state) applyTheme(state.theme);
+            },
+        },
+    ),
+);
+
+// Follow OS changes while in "system" mode.
+if (typeof window !== 'undefined') {
+    window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
+        if (usePrefs.getState().theme === 'system') applyTheme('system');
+    });
+}