User accounts

Allows for the creation of user accounts. A few notes on the specifics:

 - Experiments are the main access control objects. If you can view an experiment, you can view all its prompts/scenarios/evals. If you can edit it, you can edit or delete all of those as well.
 - Experiments are owned by Organizations in the database. Organizations can have multiple members and members can have roles of ADMIN, MEMBER or VIEWER.
 - Organizations can either be "personal" or general. Each user has a "personal" organization created as soon as they try to create an experiment. There's currently no UI support for creating general orgs or adding users to them; they're just in the database to future-proof all the ACL logic.
 - You can require that a user is signed-in to see a route using the `protectedProcedure` helper. When you use `protectedProcedure`, you also have to call `ctx.markAccessControlRun()` (or delegate to a function that does it for you; see accessControl.ts). This is to remind us to actually check for access control when we define a new endpoint.

src/pages/experiments/index.tsx

@@ -6,18 +6,44 @@ import {
   Breadcrumb,
   BreadcrumbItem,
   Flex,
+  Center,
+  Text,
+  Link,
 } from "@chakra-ui/react";
 import { RiFlaskLine } from "react-icons/ri";
 import AppShell from "~/components/nav/AppShell";
 import { api } from "~/utils/api";
 import { NewExperimentButton } from "~/components/experiments/NewExperimentButton";
 import { ExperimentCard } from "~/components/experiments/ExperimentCard";
+import { signIn, useSession } from "next-auth/react";
 
 export default function ExperimentsPage() {
   const experiments = api.experiments.list.useQuery();
 
+  const user = useSession().data;
+
+  if (user === null) {
+    return (
+      <AppShell title="Experiments">
+        <Center h="100%">
+          <Text>
+            <Link
+              onClick={() => {
+                signIn("github").catch(console.error);
+              }}
+              textDecor="underline"
+            >
+              Sign in
+            </Link>{" "}
+            to view or create new experiments!
+          </Text>
+        </Center>
+      </AppShell>
+    );
+  }
+
   return (
-    <AppShell>
+    <AppShell title="Experiments">
       <VStack alignItems={"flex-start"} m={4} mt={1}>
         <HStack w="full" justifyContent="space-between" mb={4}>
           <Breadcrumb flex={1}>