feat: add landing page with beta signup + raise KB node limit to 100

Landing page at /landing with full marketing content: hero, features,
pricing, testimonials, and beta email signup form. Beta signups email
beta@resolutionflow.com via new public endpoint. Unauthenticated users
redirect to landing instead of login. Also raises KB Accelerator node
limit from 50 to 100 to accommodate dense troubleshooting articles.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/beta_signup.py

@@ -0,0 +1,31 @@
+"""Public beta signup endpoint — no auth required."""
+
+import logging
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel, EmailStr
+from app.core.email import EmailService
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter(prefix="/beta-signup", tags=["beta"])
+
+
+class BetaSignupRequest(BaseModel):
+    email: EmailStr
+
+
+class BetaSignupResponse(BaseModel):
+    success: bool
+    message: str
+
+
+@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.",
+    )