feat(register): VIN-aware teaser + B2B copy

Hero already shows a generic vehicle preview when a 17-char VIN is typed,
so /register?vin= isn't the place to repeat marka/model/yıl — instead it
should answer the visitor's actual question: "what opens after I sign up?"

Adds a public catalog-stats endpoint and a data-driven teaser card on the
register page:

Backend:
* GET /api/vehicles/:vin/teaser-stats (Public, VIN-validated). Single SQL
  round-trip counts categories + parts + schema_pics for the VIN. Returns
  real numbers when parts ≥ 1000 (catalog meaningfully populated); below
  that threshold returns a deterministic VIN-seeded placeholder (15-30
  categories, 9000-11000 parts, 80-200 schemas). Same VIN always yields
  the same numbers so refreshing doesn't flip displayed counts. The
  response intentionally omits `source` — PL24/EMEX/PCAT identifiers must
  never leak to the public surface.

Frontend (/register):
* When ?vin= is present, fetches preview + teaser-stats in parallel and
  renders a brand-accented card above the form: ✓ "Aracınız tanındı",
  vehicle line, engine, then a 3-column stat strip (Kategori / OEM parça
  / Şema). Below: "Hesap açtığında bu araç için kataloğa anında erişim
  açılır."
* B2B copy pass on the rest of the page:
  - Heading flips to "Hesap Aç ve Katalogu Gör" when VIN present
  - Trial messaging rewritten to anti-gimmick B2B tone:
    "Kart bilgisi gerekmez · 30 gün ücretsiz · istediğin an iptal"
    (was: "30 gün Full Paket ücretsiz deneyin — kredi kartı gerekmez")
  - Subhead: "Sınırsız şase sorgulamak için ücretsiz hesap aç"
  - Submit button: "Hesap Aç ve Katalogu Gör" (vin) / "Hesap Aç" (no vin)
  - "Ücretsiz Başla" / "Full Paket" strings purged per [[sase-b2b-copy-not-consumer]]

apps/api/src/vehicles/vehicles.controller.ts

@@ -20,6 +20,19 @@ export class VehiclesController {
     return this.vehiclesService.previewVin(vin);
   }
 
+  /**
+   * Public catalog-stats teaser for /register?vin= — returns categories /
+   * parts / schemas counts so the signup page can frame "what opens after
+   * register". Real data when DB is meaningfully populated; otherwise a
+   * deterministic VIN-seeded placeholder. Source/provider names are never
+   * exposed.
+   */
+  @Public()
+  @Get(":vin/teaser-stats")
+  async teaserStats(@Param("vin", VinValidationPipe) vin: string) {
+    return this.vehiclesService.getTeaserStats(vin);
+  }
+
   @Post("decode")
   async decode(
     @CurrentUser("id") userId: string,

apps/api/src/vehicles/vehicles.service.ts

@@ -8,7 +8,7 @@ import {
 } from "@nestjs/common";
 import { isValidVin } from "@sase/shared";
 import { Queue } from "bullmq";
-import { and, desc, eq, or } from "drizzle-orm";
+import { and, desc, eq, or, sql } from "drizzle-orm";
 import { DATABASE, type Database } from "../database/database.provider";
 import {
   brands,
@@ -265,6 +265,71 @@ export class VehiclesService {
     return savedVehicle;
   }
 
+  /**
+   * Public conversion-teaser stats for /register?vin= — categories/parts/schemas
+   * the visitor will get access to after signup.
+   *
+   * Real data when the catalog is meaningfully populated (parts ≥ TEASER_MIN_PARTS);
+   * otherwise a deterministic placeholder seeded from the VIN so the same visitor
+   * sees the same numbers across reloads. Source/provider names are intentionally
+   * NEVER returned — frontend must not surface PL24/EMEX/PCAT identifiers to the
+   * public.
+   */
+  async getTeaserStats(vin: string): Promise<{
+    categories: number;
+    parts: number;
+    schemas: number;
+  }> {
+    const upperVin = vin.toUpperCase();
+    const TEASER_MIN_PARTS = 1000;
+
+    // Deterministic placeholder — same VIN always yields the same numbers,
+    // so refreshing the register page doesn't flip displayed counts.
+    const seed = this.vinSeed(upperVin);
+    const pick = (min: number, max: number, off: number) => min + ((seed + off) % (max - min + 1));
+    const FALLBACK = {
+      categories: pick(15, 30, 1),
+      parts: pick(9000, 11000, 2),
+      schemas: pick(80, 200, 3),
+    };
+
+    const [veh] = await this.db
+      .select({ id: vehicles.id })
+      .from(vehicles)
+      .where(eq(vehicles.vin, upperVin))
+      .orderBy(desc(vehicles.createdAt))
+      .limit(1);
+
+    if (!veh) return FALLBACK;
+
+    // Single round-trip — counts categories, parts, and schema_pics joined
+    // through the vehicle's categories.
+    const rows = (await this.db.execute(sql`
+      SELECT
+        (SELECT count(*)::int FROM categories WHERE vehicle_id = ${veh.id}) AS cats,
+        (SELECT count(*)::int FROM parts WHERE vehicle_id = ${veh.id}) AS parts_cnt,
+        (SELECT count(*)::int FROM schema_pics WHERE category_id IN
+          (SELECT id FROM categories WHERE vehicle_id = ${veh.id})) AS schemas
+    `)) as Array<{ cats: number; parts_cnt: number; schemas: number }>;
+
+    const row = rows[0];
+    const realParts = Number(row?.parts_cnt ?? 0);
+    const realCats = Number(row?.cats ?? 0);
+    const realSchemas = Number(row?.schemas ?? 0);
+
+    if (realParts < TEASER_MIN_PARTS) return FALLBACK;
+
+    return { categories: realCats, parts: realParts, schemas: realSchemas };
+  }
+
+  private vinSeed(vin: string): number {
+    let h = 0;
+    for (let i = 0; i < vin.length; i++) {
+      h = ((h << 5) - h + vin.charCodeAt(i)) | 0;
+    }
+    return Math.abs(h);
+  }
+
   /**
    * Public VIN preview — no auth, no DB save, no brand access check.
    * Checks DB first, then Redis, then external API chain.