Logging in returns to the page that was asked for (closes #384)

RequireAuth now sends a logged-out GET to /pages/login with its path
and query in a `next` parameter when they fit in 2048 bytes, the same
limit the login page applies. The login form carries it as a hidden
field, and a successful login redirects there when it is a path on
this site; anything else, plain or percent-encoded, goes to `/`, which
leads to the webhook list. A browser already logged in that opens the
login page goes to the same place. The navigation bar on the login
page no longer links to the login page.

Model: opus-5-5

templates/navbar.html

@@ -6,12 +6,14 @@
         </div>
 
         <!-- Mobile menu button -->
+        {{if .User}}
         <button @click="open = !open" class="md:hidden p-2 rounded-md text-gray-500 hover:bg-gray-100">
             <svg class="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                 <path x-show="!open" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 6h16M4 12h16M4 18h16"/>
                 <path x-show="open" x-cloak stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
             </svg>
         </button>
+        {{end}}
 
         <!-- Desktop navigation -->
         <div class="hidden md:flex items-center gap-4">
@@ -28,8 +30,6 @@
                 <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
                 <button type="submit" class="btn-text">Logout</button>
             </form>
-            {{else}}
-            <a href="/pages/login" class="btn-primary">Login</a>
             {{end}}
         </div>
     </div>
@@ -44,8 +44,6 @@
                 <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
                 <button type="submit" class="btn-text w-full text-left">Logout</button>
             </form>
-            {{else}}
-            <a href="/pages/login" class="btn-primary w-full">Login</a>
             {{end}}
         </div>
     </div>