feat: add upload policies, daily limits, and storage quotas

- Add environment variables to configure anonymous uploads, daily upload caps, and default user storage limits.
- Update config loader to parse and validate the new settings.
- Implement backend logic to track daily usage and active storage per user.
- Update README and `.env.example` to document the new settings and admin panels.

backend/static/css/app.css

@@ -73,6 +73,9 @@ svg {
 }
 
 .site-header {
+  position: sticky;
+  top: 0;
+  z-index: 20;
   border-bottom: 1px solid var(--border);
   background: rgba(9, 9, 11, 0.84);
   backdrop-filter: blur(14px);
@@ -241,6 +244,10 @@ h1 {
   align-self: start;
   display: grid;
   gap: 0.5rem;
+  padding: 0.75rem;
+  border: 1px solid var(--border);
+  border-radius: var(--radius);
+  background: rgba(24, 24, 27, 0.58);
 }
 
 .sidebar-link {
@@ -258,6 +265,29 @@ h1 {
   color: var(--foreground);
 }
 
+.admin-shell .app-sidebar {
+  border-color: rgba(125, 211, 252, 0.28);
+  background: linear-gradient(180deg, rgba(8, 47, 73, 0.22), rgba(24, 24, 27, 0.58));
+}
+
+.admin-shell .sidebar-link.is-active {
+  border-color: rgba(125, 211, 252, 0.42);
+  background: rgba(14, 116, 144, 0.24);
+}
+
+.admin-shell .kicker {
+  color: #7dd3fc;
+}
+
+.sidebar-logout {
+  display: grid;
+  margin: 0.75rem 0 0;
+}
+
+.sidebar-logout .button {
+  width: 100%;
+}
+
 .collection-create {
   display: grid;
   gap: 0.6rem;
@@ -270,6 +300,16 @@ h1 {
   gap: 1rem;
 }
 
+.settings-stack {
+  display: grid;
+  gap: 1rem;
+  max-width: 44rem;
+}
+
+.settings-panel {
+  box-shadow: none;
+}
+
 .compact-upload .drop-zone {
   min-height: 11rem;
 }
@@ -295,6 +335,31 @@ h1 {
   width: 10rem;
 }
 
+.settings-form {
+  display: grid;
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+  gap: 0.9rem;
+}
+
+.settings-form-narrow {
+  grid-template-columns: minmax(0, 1fr);
+}
+
+.settings-form label {
+  display: grid;
+  gap: 0.35rem;
+  color: var(--muted-foreground);
+  font-size: 0.82rem;
+}
+
+.settings-form .checkbox-field {
+  grid-column: 1 / -1;
+}
+
+.settings-form button {
+  justify-self: start;
+}
+
 .drop-zone {
   min-height: 19rem;
   display: grid;
@@ -1158,7 +1223,9 @@ pre code {
 
 @media (max-width: 720px) {
   .nav-links {
-    display: none;
+    display: inline-flex;
+    flex-wrap: wrap;
+    justify-content: flex-end;
   }
 
   .upload-view,
@@ -1181,10 +1248,16 @@ pre code {
   }
 
   .docs-grid,
-  .field-grid {
+  .field-grid,
+  .app-shell,
+  .settings-form {
     grid-template-columns: 1fr;
   }
 
+  .app-sidebar {
+    position: static;
+  }
+
   .endpoint-list div {
     grid-template-columns: 1fr;
     gap: 0.25rem;