fix(journal): centralize session-auth helpers + extract .server.ts siblings

Follow-up to PR #406 — addresses the two items deferred from the audit:

#7 — Centralize auth helpers
- New `requireSessionUser(request)` in lib/auth/session.server.ts that
  returns the user or throws a redirect to /auth/login.
- New `requireSessionUserJson(request)` companion that throws a 401 JSON
  response (for fetcher/JSON endpoints).
- Replace the repeated
    const user = await getSessionUser(request);
    if (!user) return redirect("/auth/login");
  pattern across 18 route loaders/actions. Removes the duplicated guard
  preamble and gives a single chokepoint to evolve later (e.g., for
  terms-version gating).

#8 — Extract heavy loaders into .server.ts siblings
- routes/home.tsx → home.server.ts (DB count query + listActivities +
  listRecentPublicActivities)
- routes/users.$username.tsx → users.$username.server.ts (user lookup +
  follow state + counts + listPublicRoutes/Activities + persona check)
- routes/settings.connections.tsx → settings.connections.server.ts
  (connected_services join + manifest merge)

Each route file shrinks to a thin delegator: `loader` calls
`loadXxx(request)`. The component module no longer transitively pulls
`getDb` and Drizzle schema into its import graph — Vite's tree-shake
already strips server-only code from the client bundle, but the
explicit `.server.ts` suffix makes that contract local and auditable.

Other 17 routes that mix loader/action with components are left as-is
for now: they're each small enough that the split adds churn without
buying much clarity. The pattern is documented by the three examples;
the rest can convert opportunistically when they grow.

Tests:
- lib/auth/session.server.test.ts (4 cases — redirect for missing
  cookie, redirect for ghost userId, success path, JSON 401 variant)

Full repo: pnpm typecheck, pnpm lint, pnpm test all green
(181 passed | 31 integration-gated skipped).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/journal/app/routes/settings.connections.tsx

@@ -1,11 +1,7 @@
-import { data, redirect, useSearchParams } from "react-router";
+import { data, useSearchParams } from "react-router";
 import { useTranslation } from "react-i18next";
-import { eq } from "drizzle-orm";
 import type { Route } from "./+types/settings.connections";
-import { getSessionUser } from "~/lib/auth/session.server";
-import { getDb } from "~/lib/db";
-import { connectedServices } from "@trails-cool/db/schema/journal";
-import { getAllManifests } from "~/lib/connected-services";
+import { loadConnectionsSettings } from "./settings.connections.server";
 
 const KNOWN_ERRORS = ["too_many_tokens", "sync_failed", "generic"] as const;
 type KnownError = (typeof KNOWN_ERRORS)[number];
@@ -18,30 +14,7 @@ export function meta() {
 }
 
 export async function loader({ request }: Route.LoaderArgs) {
-  const user = await getSessionUser(request);
-  if (!user) throw redirect("/auth/login");
-
-  const db = getDb();
-  const connections = await db
-    .select({
-      provider: connectedServices.provider,
-      providerUserId: connectedServices.providerUserId,
-    })
-    .from(connectedServices)
-    .where(eq(connectedServices.userId, user.id));
-
-  const providers = getAllManifests().map((m) => {
-    const conn = connections.find((c) => c.provider === m.id);
-    return {
-      id: m.id,
-      name: m.displayName,
-      connected: !!conn,
-      providerUserId: conn?.providerUserId,
-      connectUrl: m.connectUrl ?? null,
-    };
-  });
-
-  return data({ providers });
+  return data(await loadConnectionsSettings(request));
 }
 
 export default function ConnectionsSettings({ loaderData }: Route.ComponentProps) {