Add multi-tag filtering with active tag display, optimize directory browsing performance, and improve mobile editor UI

frontend/style.css

@@ -84,6 +84,7 @@ a:hover {
 .header {
   display: flex;
   align-items: center;
+  justify-content: space-between;
   gap: 12px;
   padding: 10px 20px;
   background: var(--bg-secondary);
@@ -93,6 +94,28 @@ a:hover {
   transition: background 200ms ease;
 }
 
+.header-left {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  flex: 1;
+  min-width: 0;
+}
+
+.header-center {
+  display: flex;
+  justify-content: center;
+  flex: 2;
+  max-width: 600px;
+}
+
+.header-right {
+  display: flex;
+  justify-content: flex-end;
+  flex: 1;
+  min-width: 0;
+}
+
 .hamburger-btn {
   display: none;
   background: none;
@@ -114,7 +137,6 @@ a:hover {
   font-size: 1.15rem;
   color: var(--accent);
   white-space: nowrap;
-  margin-right: auto;
   display: flex;
   align-items: center;
   gap: 8px;
@@ -128,7 +150,7 @@ a:hover {
 }
 
 .search-wrapper {
-  flex: 1;
+  width: 100%;
   max-width: 520px;
   position: relative;
 }
@@ -157,6 +179,38 @@ a:hover {
   pointer-events: none;
 }
 
+.active-tags {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  margin-top: 8px;
+  min-height: 0;
+}
+
+.active-tag {
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  padding: 3px 8px;
+  background: var(--tag-bg);
+  color: var(--tag-text);
+  border-radius: 4px;
+  font-family: 'JetBrains Mono', monospace;
+  font-size: 0.75rem;
+  cursor: pointer;
+  transition: opacity 150ms ease;
+}
+.active-tag:hover {
+  opacity: 0.7;
+}
+.active-tag .remove-icon {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 14px;
+  height: 14px;
+}
+
 .header-menu {
   position: relative;
 }
@@ -569,8 +623,15 @@ a:hover {
   color: var(--tag-text);
   border-radius: 4px;
   font-family: 'JetBrains Mono', monospace;
-  font-size: 0.78rem;
+  font-size: 0.75rem;
+  margin-right: 6px;
+  margin-bottom: 4px;
   cursor: pointer;
+  transition: opacity 150ms ease, transform 100ms ease;
+}
+.file-tag:hover {
+  opacity: 0.8;
+  transform: translateY(-1px);
 }
 .file-actions {
   margin-top: 8px;
@@ -980,15 +1041,27 @@ a:hover {
   
   .editor-header {
     padding: 10px 12px;
+    position: sticky;
+    top: 0;
+    z-index: 10;
   }
   
   .editor-title {
     font-size: 0.85rem;
   }
   
+  .editor-actions {
+    gap: 6px;
+  }
+  
   .editor-btn {
     font-size: 0.75rem;
-    padding: 5px 10px;
+    padding: 8px;
+    min-width: 36px;
+  }
+  
+  .editor-btn-text {
+    display: none;
   }
   
   .editor-body {
@@ -1044,6 +1117,20 @@ body.resizing-v {
     padding: 8px 10px;
   }
 
+  .header-left {
+    flex: 0 0 auto;
+    gap: 8px;
+  }
+
+  .header-center {
+    flex: 1;
+    max-width: none;
+  }
+
+  .header-right {
+    flex: 0 0 auto;
+  }
+
   .header-logo {
     font-size: 0.95rem;
     gap: 6px;
@@ -1051,7 +1138,6 @@ body.resizing-v {
 
   .search-wrapper {
     max-width: none;
-    flex: 1;
   }
 
   .search-wrapper input {