feat(sales): redirect beta-signup to /register; queue waitlist emails

Phase 2 retires the public beta-signup form in favor of the self-serve
register flow. The /api/v1/beta-signup POST endpoint stays mounted but
now responds with 307 to /register?from=beta so any external links keep
working and analytics can tag signup origin via the from query param.

Note: there is no beta_signup table in the schema — the original
endpoint only fired an email notification, so there is no waitlist to
read and no migration to run for the email-sent_at field. The one-off
admin script in the spec is therefore a no-op and is intentionally not
added here.

- Replace POST /beta-signup handler with RedirectResponse(307)
- Drop the EmailService.send_beta_signup_notification call (the user is
  now redirected into the register flow, which has its own email path)
- Add tests/test_beta_signup_redirect.py covering the 307 + Location

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/api/endpoints/beta_signup.py

@@ -1,31 +1,44 @@
-"""Public beta signup endpoint — no auth required."""
+"""Legacy beta signup endpoint — redirects to /register?from=beta.
+
+Phase 2 (self-serve signup) makes the public register flow the canonical
+front door. The old `/api/v1/beta-signup` POST endpoint is kept mounted to
+preserve any external links that still hit it, but now responds with a
+307 Temporary Redirect to `/register?from=beta` so the user lands in the
+real signup flow. The `?from=beta` marker lets the frontend tag the
+signup origin for analytics.
+
+Note: there is no `beta_signup` database table — the original endpoint
+only fired a notification email. There is therefore no waitlist to email
+and no migration to run when retiring the endpoint.
+"""
 
 import logging
-from fastapi import APIRouter, HTTPException
-from pydantic import BaseModel, EmailStr
-from app.core.email import EmailService
+
+from fastapi import APIRouter
+from fastapi.responses import RedirectResponse
+
+from app.core.config import settings
 
 logger = logging.getLogger(__name__)
 
 router = APIRouter(prefix="/beta-signup", tags=["beta"])
 
-
-class BetaSignupRequest(BaseModel):
-    email: EmailStr
+# Local-dev fallback when FRONTEND_URL isn't configured. The redirect must
+# be absolute — a relative URL would resolve against the API origin
+# (api.resolutionflow.com), which has no /register page.
+_DEFAULT_FRONTEND_URL = "http://localhost:5173"
 
 
-class BetaSignupResponse(BaseModel):
-    success: bool
-    message: str
+@router.post("", include_in_schema=False)
+async def beta_signup_redirect() -> RedirectResponse:
+    """Redirect legacy beta-signup POST to the public register page.
 
-
-@router.post("", response_model=BetaSignupResponse)
-async def beta_signup(data: BetaSignupRequest):
-    """Collect beta interest — sends notification to beta@resolutionflow.com."""
-    sent = await EmailService.send_beta_signup_notification(data.email)
-    if not sent:
-        logger.warning("Beta signup recorded (email delivery skipped): %s", data.email)
-    return BetaSignupResponse(
-        success=True,
-        message="Thanks! We'll be in touch with beta access details.",
+    Returns 307 so any client following the redirect preserves the HTTP
+    method; the frontend treats `/register?from=beta` as the canonical
+    entry point and reads the `from` query param for analytics.
+    """
+    frontend_url = settings.FRONTEND_URL or _DEFAULT_FRONTEND_URL
+    return RedirectResponse(
+        url=f"{frontend_url}/register?from=beta",
+        status_code=307,
     )