Make the window a fixed shell with no scrollbars

Lock html/body/#root to the viewport and hide scrollbars everywhere; the
content area fills its space instead of scrolling the page, and the logs
stream scrolls within its own pane. Add a min window size so the layout
can't be shrunk below where everything fits.

src-tauri/tauri.conf.json

@@ -15,6 +15,8 @@
         "title": "TutaBridge",
         "width": 700,
         "height": 520,
+        "minWidth": 700,
+        "minHeight": 520,
         "resizable": true,
         "center": true
       }

ui/src/App.css

@@ -79,8 +79,17 @@
 /* ── Content ── */
 .app-content {
   flex: 1;
-  overflow-y: auto;
+  min-height: 0;
+  overflow: hidden;
   padding: 24px;
+  display: flex;
+  flex-direction: column;
+}
+
+/* The single active panel fills the content area. */
+.app-content > * {
+  flex: 1;
+  min-height: 0;
 }
 
 /* ── Shared ── */
@@ -518,7 +527,7 @@ button.small {
   max-width: none;
   display: flex;
   flex-direction: column;
-  height: calc(100vh - 120px);
+  min-height: 0;
 }
 
 .logs-header {
@@ -534,6 +543,7 @@ button.small {
 
 .logs-container {
   flex: 1;
+  min-height: 0;
   overflow-y: auto;
   background: var(--surface-container);
   border: 1px solid var(--outline-variant);

ui/src/index.css

@@ -77,14 +77,21 @@
   }
 }
 
+/* App is a fixed shell: no scrollbars anywhere. Scrollable regions (logs)
+   still scroll via wheel/keys, just without visible bars. */
 * {
   box-sizing: border-box;
+  scrollbar-width: none;
 }
 
-body {
+*::-webkit-scrollbar {
-  margin: 0;
+  display: none;
 }
 
+html,
+body,
 #root {
   height: 100vh;
+  margin: 0;
+  overflow: hidden;
 }