feat(web): redesign — three-pane desktop, mobile tab bar, search

Implements the approved design proposal across every screen.

- Layout: feeds · list · reader panes on desktop (≥1280px), list + reader
  with the feeds in a drawer on tablets, one column with a bottom tab bar
  (À lire, Focus, Favoris, Flux) on phones.
- List: dense rows with an unread dot, feed initial and square thumbnail
  instead of large cards; touch swipe reveals the action (→ lu, ← favori).
  The magazine grid stays available as a view toggle.
- Reader: inline pane on desktop, full screen on phones with a bottom
  action bar (favori, partager, original, Suivant); collapsible "Résumé IA"
  block; "Aa" settings become a bottom sheet on phones.
- Search: the existing /articles/search endpoint gets a UI — ⌘K / "/"
  palette on desktop, full screen on phones, with recent searches.
- Mobile "Mes flux" screen: views, subscriptions with errors, theme,
  OPML import/export, logout.
- Focus mode: progress bar, counter and labelled buttons.
- Tokens: new paper / deep-forest palette (all text ≥4.5:1), Newsreader +
  Inter replace Playfair + Lora (two families instead of four), shared
  Icon and FeedAvatar components.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UPyU2LbJ2rTrsgZqQKhH3j

web/index.html

@@ -4,7 +4,7 @@
 <head>
   <meta charset="UTF-8" />
   <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
-  <meta name="theme-color" content="#F7F4EC" />
+  <meta name="theme-color" content="#F6F4EE" />
   <meta name="viewport" content="width=device-width, initial-scale=1.0, viewport-fit=cover" />
   <meta name="description"
     content="FlowReader - Votre édition quotidienne pour une lecture plaisir et sans distractions." />