feat(growth): B2B segment kapısı + funnel-bucket A/B deneyi (Kova B)

Fix (herkes, flag'siz): evrensel post-auth segment kapısı (segment-gate.tsx).
Kayıtların ~%41'i segmentsizdi çünkü login.tsx Google OAuth segment adımını
atlıyordu. Yeni kullanıcıya zorunlu (açığı kapatır), mevcut segmentsize
7g-cooldown'lu yumuşak prompt (~538 backfill). Segment localStorage +
PostHog person prop (b2b_segment); backend persist faz 2.

Kova B (funnel-bucket flag, b2b_qualified): trial-value-upsell'e segmente-özel
Meta-kanıtlı kopya (iade / yanlış-parça / sınırsız-şase). Flag SADECE banner
görünürken okunur → deney maruziyeti = gerçekten gören aktif trial'lar.
vehicle_owner / bilinmeyen segment → nötr control kopya (ürün kararı).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/web/src/components/auth/segment-gate.tsx

@@ -0,0 +1,145 @@
+import { SegmentQualifier } from "@/components/auth/segment-qualifier";
+import { useAuth } from "@/hooks/use-auth";
+import { capture, setPeopleProperties } from "@/lib/posthog";
+import { Button } from "@sase/ui";
+import { useLocation } from "@tanstack/react-router";
+import { useEffect, useState } from "react";
+
+/**
+ * Universal post-auth segment gate.
+ *
+ * The register page gates segment selection behind the form, but that only
+ * covers email + register-page-OAuth signups. A user who starts Google OAuth
+ * from the LOGIN page (login.tsx) gets an account created server-side and lands
+ * on the dashboard with no segment ever chosen — this is the bulk of the ~41%
+ * of signups with a null segment. Segment isn't persisted server-side (only
+ * localStorage + a PostHog person property), so we enforce it here at the one
+ * chokepoint every authenticated user passes through: the dashboard.
+ *
+ * Behaviour (product decision 2026-07-27):
+ *  - New users (account created in the last few minutes → the login-OAuth gap):
+ *    MANDATORY, non-dismissible modal.
+ *  - Existing segment-less users (the ~538 backfill): SOFT, dismissible with a
+ *    cooldown so we re-ask later without nagging or blocking active/paying users.
+ *
+ * This is a baseline fix shipped to everyone — NOT the `funnel-bucket` A/B
+ * experiment (that gates the tailored value/upgrade experience separately).
+ */
+const SEGMENT_KEY = "sase-b2b-segment";
+const DISMISS_UNTIL_KEY = "sase-b2b-segment-prompt-until";
+// Account younger than this ⇒ treat as a fresh signup (mandatory). Generous so
+// the signup → first dashboard load always counts, even with a slow OAuth hop.
+const NEW_USER_WINDOW_MS = 15 * 60 * 1000;
+// How long a "Daha sonra" dismissal silences the soft prompt for existing users.
+const DISMISS_COOLDOWN_MS = 7 * 24 * 60 * 60 * 1000;
+
+function readSegment(): string | null {
+  try {
+    return localStorage.getItem(SEGMENT_KEY);
+  } catch {
+    return null;
+  }
+}
+
+export function SegmentGate() {
+  const { user, isLoading } = useAuth();
+  const location = useLocation();
+  const [open, setOpen] = useState(false);
+  const [mandatory, setMandatory] = useState(false);
+
+  useEffect(() => {
+    // Only inside the app, only once the session has resolved to a real user.
+    if (isLoading || !user) {
+      setOpen(false);
+      return;
+    }
+    if (!location.pathname.startsWith("/dashboard")) {
+      setOpen(false);
+      return;
+    }
+    // Already segmented — nothing to do. (Register writes this pre-redirect, so
+    // email + register-OAuth signups never see the gate.)
+    if (readSegment()) {
+      setOpen(false);
+      return;
+    }
+
+    const createdAt = user.createdAt ? new Date(user.createdAt).getTime() : 0;
+    const isNew = createdAt > 0 && Date.now() - createdAt < NEW_USER_WINDOW_MS;
+
+    if (isNew) {
+      setMandatory(true);
+      setOpen(true);
+      return;
+    }
+
+    // Existing segment-less user: honour the soft-dismiss cooldown.
+    let dismissedUntil = 0;
+    try {
+      dismissedUntil = Number(localStorage.getItem(DISMISS_UNTIL_KEY)) || 0;
+    } catch {
+      dismissedUntil = 0;
+    }
+    if (Date.now() < dismissedUntil) {
+      setOpen(false);
+      return;
+    }
+    setMandatory(false);
+    setOpen(true);
+  }, [user, isLoading, location.pathname]);
+
+  if (!open) return null;
+
+  function handleSelect(seg: string) {
+    try {
+      localStorage.setItem(SEGMENT_KEY, seg);
+    } catch {
+      // localStorage unavailable — still fire analytics below.
+    }
+    // `source` distinguishes the login-OAuth gap fill from the backfill so we can
+    // measure each in PostHog; mirrors register.tsx's signup_segment_selected.
+    capture("signup_segment_selected", {
+      segment: seg,
+      source: mandatory ? "post_signup_gate" : "backfill_gate",
+    });
+    setPeopleProperties({ b2b_segment: seg });
+    setOpen(false);
+  }
+
+  function handleDismiss() {
+    try {
+      localStorage.setItem(DISMISS_UNTIL_KEY, String(Date.now() + DISMISS_COOLDOWN_MS));
+    } catch {
+      // best-effort
+    }
+    capture("signup_segment_prompt_dismissed");
+    setOpen(false);
+  }
+
+  return (
+    <div
+      className="fixed inset-0 z-[60] flex items-center justify-center overflow-y-auto bg-background/80 p-4 backdrop-blur-sm"
+      // biome-ignore lint/a11y/useSemanticElements: overlay modal — role="dialog"+aria-modal is the correct ARIA here; a native <dialog> would need imperative showModal() plumbing this SPA overlay doesn't use
+      role="dialog"
+      aria-modal="true"
+      aria-label="İşletme türü seçimi"
+    >
+      <div className="my-auto w-full max-w-md rounded-2xl border border-border bg-card p-6 shadow-xl">
+        <div>
+          <h2 className="text-xl font-bold tracking-tight">Bu platform kimler için?</h2>
+          <p className="mt-2 text-sm text-muted-foreground">
+            İşletmeni seç — sana uygun sınırsız şase sorgulama erişimini açalım.
+          </p>
+        </div>
+        <div className="mt-5">
+          <SegmentQualifier onSelect={handleSelect} />
+        </div>
+        {!mandatory && (
+          <Button variant="ghost" className="mt-3 w-full" onClick={handleDismiss}>
+            Daha sonra
+          </Button>
+        )}
+      </div>
+    </div>
+  );
+}