feat: public landing page with magic login, brand palette and demo build flag

Adds a public funnel landing at `/` and moves the login to `/login`, rebuilt
around the panel's own colors instead of an invented palette.

Landing (`src/components/landing/`, one section per file, no props):
- Seven funnel sections composed by `LandingPage`. The hero's eight swatches are
  literally `PIE_COLORS` from `DashboardPage`, the same hex values the seed hands
  to avatars and services, so "your colors become your numbers" is literal.
- `BrandMark` becomes the single source for the logo, replicating
  `public/favicon.svg`. Blue is the action surface, orange only ever marks.
- `NotebookVisual` is the one deliberate exception to the palette: it is what the
  product replaces.
- Copy drops all system vocabulary; motion comes from `src/lib/motion.ts` with a
  single easing, and reduced-motion resolves `initial` to the final state so a
  never-firing `whileInView` cannot leave a section invisible forever.

Routing and bundle:
- `homePathFor` is the single definition of each role's destination.
- Landing, login, dashboard and calendar load lazily. Eager, the login dragged
  framer-motion (~40 KB gz) into every panel load and the landing downloaded
  recharts + FullCalendar (~187 KB gz) without charting anything. `clsx` is
  pinned to the `react` chunk because Rollup otherwise assigns it to `charts`,
  making the entry import 111 KB gz for a 200-byte utility.

Responsiveness (iPhone/iPad), verified with `npm run audit:responsive`:
- No touch form field below 16px, `dvh` height utilities, safe-area insets, and
  40px touch targets keyed off `pointer: coarse` rather than `sm:`.
- New `.ld-gutter`: `.safe-x` lives outside `@layer` and beats Tailwind's `px-*`,
  so it left the login's side padding at 0 on anything but an iPhone in
  landscape. No overflow check could see it — there was no overflow, just zero
  margin. The audit now guards it with a `gutter` check.
- `shell-height` no longer fires on pages that legitimately scroll; the static
  `raw-viewport-unit` scan covers those instead.

Production build:
- The Dockerfile now sets `VITE_DEMO_UI=1` as a build arg. `DEMO` is a build-time
  constant, so without it Vite eliminated the magic login and the "Ver como…"
  switcher: the deployed landing promised "no registration" and led to an empty
  form. Verified by building both ways and diffing the bundle.
- Service worker cache bumped to v2 so the orphaned pre-landing chunks get purged
  from returning visitors' caches.

Verified: typecheck clean; unit 39/39, e2e 33/33, admin 17/17, booking 12/12,
landing 13/13 (WebKit), PWA passed against the real production build.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

src/lib/useSidebarCollapsed.ts

@@ -0,0 +1,43 @@
+import { useCallback, useEffect, useState } from "react";
+
+const KEY = "ap_sidebar_collapsed";
+
+function read(): boolean {
+  if (typeof window === "undefined") return false;
+  try {
+    return window.localStorage.getItem(KEY) === "1";
+  } catch {
+    return false; // Safari en modo privado puede lanzar al leer localStorage.
+  }
+}
+
+/**
+ * Colapso de la barra lateral en pantallas grandes (lg+), recordado entre
+ * sesiones. En iPad Pro portrait (1024px) la barra expandida se lleva 256px de
+ * los 1024 disponibles, así que poder colapsarla a solo iconos es lo que más
+ * ancho devuelve al contenido.
+ */
+export function useSidebarCollapsed() {
+  const [collapsed, setCollapsed] = useState(read);
+
+  const toggle = useCallback(() => setCollapsed((c) => !c), []);
+
+  useEffect(() => {
+    try {
+      window.localStorage.setItem(KEY, collapsed ? "1" : "0");
+    } catch {
+      /* sin persistencia si el almacenamiento está bloqueado */
+    }
+  }, [collapsed]);
+
+  // Mantiene ambos shells (app y admin) en sincronía si se abren en dos pestañas.
+  useEffect(() => {
+    const onStorage = (e: StorageEvent) => {
+      if (e.key === KEY && e.newValue !== null) setCollapsed(e.newValue === "1");
+    };
+    window.addEventListener("storage", onStorage);
+    return () => window.removeEventListener("storage", onStorage);
+  }, []);
+
+  return { collapsed, toggle };
+}