Update system name and references from TeaBoy to Tx

Replaces all user-facing instances of "TeaBoy" with "Tx" across the application, including titles, locale files, database settings, seed data, and API documentation. Also updates internal storage keys and session secrets to remove the old branding.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 77cfe984-2c65-4152-bb7a-0df28274fe66
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 07b19cb0-11b5-4be9-8932-ae4820eb73b8
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/c3c252e4-c83d-40ca-9fff-99a3ea60701e/77cfe984-2c65-4152-bb7a-0df28274fe66/HxTkDPZ
Replit-Helium-Checkpoint-Created: true

artifacts/api-server/tests/groups-crud.test.mjs

@@ -114,7 +114,7 @@ test("GET /api/groups requires admin (regular user gets 403)", async () => {
   assert.equal(res.status, 403);
 });
 
-test("admin lists default seed groups including Admins, TeaBoy, Everyone", async () => {
+test("admin lists default seed groups including Admins, Tx, Everyone", async () => {
   const res = await fetch(`${API_BASE}/api/groups`, {
     headers: { Cookie: adminCookie },
   });
@@ -122,7 +122,7 @@ test("admin lists default seed groups including Admins, TeaBoy, Everyone", async
   const list = await res.json();
   const names = new Set(list.map((g) => g.name));
   assert.ok(names.has("Admins"));
-  assert.ok(names.has("TeaBoy"));
+  assert.ok(names.has("Tx"));
   assert.ok(names.has("Everyone"));
 });