fix: Include query parameters in link back to login on register page

src/web/pages/templates/book.html.j2

@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <meta charset="UTF-8" />
+        <title>The Book of Matrix, 4:15</title>
+        <meta name="viewport" content="width=device-width, initial-scale=1" />
+        <meta name="robots" content="noindex" />
+
+        <link rel="icon" href="{{ crate::ROUTE_PREFIX }}/resources/logo.svg">
+        <link rel="stylesheet" href="{{ crate::ROUTE_PREFIX }}/resources/book.css">
+    </head>
+
+    <body>
+        <main>
+            And the <em>Conduit</em> was greatly diminished, and it Rusted slowly in the dark, and its builders
+            were scattered to the four corners of the Network, and all seemed to be lost for those
+            who would stand against the <em>Great Homogeneous Mind</em> of the Federation. But lo!
+            From its corpse there formed a <em>New Coalition</em>, a team to <em>Continue</em> the legacy of the Conduit,
+            and their works pushed back the <em>Synapses of the Great Mind</em>, and illuminated the darkest corners
+            of the <em>Specification</em>, for the betterment of the Network at large. ◈
+        </main>
+    </body>
+</html>

src/web/pages/templates/register.html.j2

@@ -80,7 +80,8 @@ Sign up
             </form>
             {% if !is_first_run %}
                 <div class="centered-links">
-                    <a href="{{ crate::ROUTE_PREFIX }}/account/login">I already have an account</a>
+                    {% let query = next.as_ref().map(serde_urlencoded::to_string).transpose().unwrap().unwrap_or_default() %}
+                    <a href="{{ crate::ROUTE_PREFIX }}/account/login?{{ query }}">I already have an account</a>
                 </div>
             {% endif %}
         {% when RegisterBody::DetailsPrompt { username, require_email, flow, terms, validation_errors } %}