Stop treating login/save-progress as a 48-character email limit.

The overlay was failing Zod on preset method-card support text attached with the draft; raise that cap, allow RFC-length emails, and drop Back to home from the overlay.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/contexts/AuthModalContext.test.tsx

@@ -96,8 +96,8 @@ describe("AuthModalProvider (header overlay)", () => {
       screen.getByRole("heading", { name: /log in to communityrule/i }),
     ).toBeInTheDocument();
     expect(
-      screen.getByRole("link", { name: /back to home/i }),
-    ).toBeInTheDocument();
+      screen.queryByRole("link", { name: /back to home/i }),
+    ).not.toBeInTheDocument();
   });
 
   it("closes overlay when closeLogin is called", async () => {