feat (ui): compacte IDE-sidebar tree view voor Files tabblad

- Vervang kaart-stijl folder-rijen door compacte, platte rijen (2px padding, geen border)
- Verwijder badge-tellers (📁 N, 📄 N) uit folder-rijen
- Voeg .btn.tiny toe voor kleine actieknoppen (+/✕) in boom
- Alle mappen standaard ingeklapt; localStorage behoudt uitgeklapte staat
- file-entry hover highlight; verwijder bottom-border per rij

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

webui/html/assets/css/app.css

@@ -250,6 +250,7 @@ header{
 .btn:hover{background: var(--btn2)}
 .btn:active{transform: translateY(1px)}
 .btn.small{padding:7px 9px; border-radius: 10px}
+.btn.tiny{padding:1px 5px; border-radius: 4px; font-size:11px; line-height:16px;}
 .btn.ghost{background: transparent}
 .btn.ok{border-color: rgba(45,212,191,.6)}
 .btn.bad{border-color: rgba(251,113,133,.6)}
@@ -643,29 +644,30 @@ pre{
     .sidebar .navLabel { display: none; }
     .sidebar .tab { justify-content: center; }
 }
-/* Files tree (Portainer-ish) */
+/* Files tree (IDE sidebar stijl) */
 .file-folder-row{
     display:flex;
     align-items:center;
     justify-content:space-between;
-    gap:10px;
+    gap:6px;
     cursor:pointer;
     user-select:none;
 
-    padding: 10px 12px;
-    border: 1px solid var(--card-border);
-    border-radius: 12px;
-    background: var(--folder-bg);
-    transition: background .12s ease, border-color .12s ease, transform .06s ease;
+    padding: 2px 6px;
+    border: none;
+    border-radius: 4px;
+    background: transparent;
+    transition: background .1s ease;
+    line-height: 22px;
+    font-weight: 600;
 }
 
 .file-folder-row:hover{
     background: var(--folder-hover);
-    border-color: rgba(96,165,250,.35);
 }
 
-.file-folder-row:active{
-    transform: translateY(1px);
+.file-entry:hover{
+    background: var(--folder-hover);
 }
 
 .file-folder-left{
@@ -697,19 +699,19 @@ pre{
 
 .file-folder-files{
     margin-left: 0;
-    margin-top: 6px;
-    padding-left: 12px;
-    border-left: 1px dashed var(--soft-line);
+    margin-top: 0;
+    padding-left: 0;
+    border-left: none;
 }
 
 .file-entry{
     display:flex;
     align-items:center;
     justify-content:space-between;
-    gap:10px;
-    padding:4px 0;
-    border-bottom:1px dashed var(--soft-line);
-    border-radius: 8px;
+    gap:6px;
+    padding: 2px 6px;
+    border-radius: 4px;
+    line-height: 22px;
 }
 .file-entry-name{
     cursor:pointer;