feat: particle cloud (no discrete dots) + geo-IP country preselect on login

Two coordinated polish moves the owner asked for.

## 1. Hero particle field — "no white dots, just a glow that follows the mouse and is always in motion"

Previous tuning (uPointSize 2.8, uBaseAlpha 0.6) gave discrete indigo
dots that additively saturated to near-white in dense clusters. The
owner wanted no granular dots visible at all — a continuous indigo
cloud that the cursor pulls toward itself.

Changes:

- **Render fragment**: replaced the anti-aliased disc SDF
  (`smoothstep(0.5, 0.42, d)` — hard edge) with a Gaussian falloff
  (`exp(-d * d * 6.0)` — smooth blob, no edge). Each particle is now
  a soft volume that blends seamlessly with neighbours.

- **Sim fragment**: replaced the outward-gradient ring push with a
  mouse-halo attraction. Particles drift toward an ideal radius
  (~0.20) around the cursor, with exp-bell falloff so they don't
  collapse onto the cursor or feel influenced from across the canvas.
  `ringField()` helper is now unused but kept for future use.

- **JS uniforms**: `uPointSize` 2.8→14 (256-tier) / 3.6→20 (128-tier);
  `uBaseAlpha` 0.6→0.055. Individual particles are below the
  perception threshold for "dot" but 65k of them additively composite
  into a continuous cloud. With the much lower per-particle alpha,
  the cumulative brightness never saturates to white.

- **ParticleField tick loop**: asymmetric ring-active fade — `alpha
  = 0.14` ramping in (fast cursor response), `0.012` decaying out
  (slow glow trail after the pointer moves away). Matches the brief
  "glow longer + attractive to mouse but always in motion".

- **ParticleHero index.tsx**: added an always-on indigo radial
  gradient behind the WebGL canvas, so the hero never reads as
  visually empty between frames — the canvas additively paints the
  dynamic cloud on top. Removed the white-dot stipple from the
  static fallback (it was the most likely source of the "weisse
  punkte" complaint for any visitor on the fallback path).

## 2. SMS login — pre-select country picker from visitor's geo-IP

The country picker on `/login` previously defaulted to `'CH'` for
everyone. Visitors from DE / AT / US / etc. had to manually scroll
to their dial code — small friction but it sits on the highest-stakes
conversion step in the funnel.

- **New API route** `apps/api/src/routes/geo.ts` →
  `GET /v1/geo/country` returns `{ country: 'CH' | 'DE' | … | null }`
  by reading Cloudflare's `CF-IPCountry` header. Public, no auth —
  reading a 2-letter country code from a geo-IP header isn't PII
  under GDPR / DSG. `'XX'` and `'T1'` (CF's "unknown" + Tor) are
  normalised to `null`. Outside CF (dev), header is missing → null.

- **Login page** picks up the result in the existing `useEffect`,
  guards against codes not in our country list, and calls `setCountry`
  to override the `'CH'` default. Stays at `'CH'` if the detection
  fails or the visitor is on a Tor exit. Verified live: the endpoint
  returns `{"country":"DE"}` from CF's German edge.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/components/particle-hero/index.tsx

@@ -136,28 +136,41 @@ export function ParticleHero() {
     return () => reduce.removeEventListener('change', onReduceChange);
   }, []);
 
-  // Static fallback: radial indigo glow + faint dotted mask.
-  // Used both for 'unknown' (pre-hydration) and 'fallback'.
+  // Static fallback: pure indigo radial glow, no dot grid. The
+  // dot-mask was confusing — it read as "stippled white texture"
+  // against the indigo glow rather than as resting particles. The
+  // cleaner, dotless gradient holds up better as a fallback.
   if (cap.kind !== 'webgl') {
     return (
       <div
         aria-hidden="true"
         className="absolute inset-0 size-full overflow-hidden"
         style={{
-          backgroundImage: [
-            // Soft indigo glow centered on the hero
-            'radial-gradient(60% 80% at 50% 45%, rgba(99,102,241,0.18), rgba(99,102,241,0) 70%)',
-            // Very faint dotted texture — reads as "field of particles
-            // at rest" rather than a flat gradient.
-            'radial-gradient(circle at 1px 1px, rgba(255,255,255,0.05) 1px, transparent 1.5px)',
-          ].join(', '),
-          backgroundSize: '100% 100%, 24px 24px',
+          background:
+            'radial-gradient(65% 80% at 50% 45%, rgba(99,102,241,0.22), rgba(99,102,241,0) 72%)',
         }}
       />
     );
   }
 
-  return <ParticleField textureSize={cap.textureSize} motionScale={cap.motionScale} />;
+  // WebGL path: an always-on indigo radial behind the canvas so the
+  // hero never feels visually empty (even between frames, even when the
+  // pointer is far away). The canvas paints the dynamic cloud + halo
+  // additively on top of this baseline glow — the result is "longer
+  // glow" without needing the simulation to keep a permanent ring on.
+  return (
+    <>
+      <div
+        aria-hidden="true"
+        className="pointer-events-none absolute inset-0 size-full"
+        style={{
+          background:
+            'radial-gradient(70% 85% at 50% 48%, rgba(99,102,241,0.22), rgba(99,102,241,0) 72%)',
+        }}
+      />
+      <ParticleField textureSize={cap.textureSize} motionScale={cap.motionScale} />
+    </>
+  );
 }
 
 export default ParticleHero;