feat: add Toolbar component with active state and formatting buttons

src/lib/editor/Toolbar.svelte

@@ -0,0 +1,135 @@
+<script lang="ts">
+  import type { Editor } from '@tiptap/core';
+
+  let { editor }: { editor: Editor | null } = $props();
+</script>
+
+<div class="toolbar">
+  {#if editor}
+    <div class="toolbar-group">
+      <button
+        class:active={editor.isActive('bold')}
+        onclick={() => editor?.chain().focus().toggleBold().run()}
+        title="Bold (Ctrl+B)"
+      >
+        <strong>B</strong>
+      </button>
+      <button
+        class:active={editor.isActive('italic')}
+        onclick={() => editor?.chain().focus().toggleItalic().run()}
+        title="Italic (Ctrl+I)"
+      >
+        <em>I</em>
+      </button>
+      <button
+        class:active={editor.isActive('underline')}
+        onclick={() => editor?.chain().focus().toggleUnderline().run()}
+        title="Underline (Ctrl+U)"
+      >
+        <u>U</u>
+      </button>
+    </div>
+
+    <div class="toolbar-separator"></div>
+
+    <div class="toolbar-group">
+      <button
+        class:active={editor.isActive('heading', { level: 1 })}
+        onclick={() => editor?.chain().focus().toggleHeading({ level: 1 }).run()}
+        title="Heading 1"
+      >
+        H1
+      </button>
+      <button
+        class:active={editor.isActive('heading', { level: 2 })}
+        onclick={() => editor?.chain().focus().toggleHeading({ level: 2 }).run()}
+        title="Heading 2"
+      >
+        H2
+      </button>
+      <button
+        class:active={editor.isActive('heading', { level: 3 })}
+        onclick={() => editor?.chain().focus().toggleHeading({ level: 3 }).run()}
+        title="Heading 3"
+      >
+        H3
+      </button>
+    </div>
+
+    <div class="toolbar-separator"></div>
+
+    <div class="toolbar-group">
+      <button
+        onclick={() => editor?.chain().focus().undo().run()}
+        disabled={!editor.can().undo()}
+        title="Undo (Ctrl+Z)"
+      >
+        ↩
+      </button>
+      <button
+        onclick={() => editor?.chain().focus().redo().run()}
+        disabled={!editor.can().redo()}
+        title="Redo (Ctrl+Shift+Z)"
+      >
+        ↪
+      </button>
+    </div>
+  {/if}
+</div>
+
+<style>
+  .toolbar {
+    display: flex;
+    align-items: center;
+    gap: 0.25rem;
+    padding: 0.5rem 1rem;
+    background: var(--color-toolbar-bg);
+    border-bottom: 1px solid var(--color-border);
+    position: sticky;
+    top: 0;
+    z-index: 10;
+  }
+
+  .toolbar-group {
+    display: flex;
+    gap: 2px;
+  }
+
+  .toolbar-separator {
+    width: 1px;
+    height: 1.5rem;
+    background: var(--color-border);
+    margin: 0 0.5rem;
+  }
+
+  button {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    min-width: 2rem;
+    height: 2rem;
+    padding: 0 0.5rem;
+    border: none;
+    border-radius: var(--radius);
+    background: transparent;
+    color: var(--color-text);
+    font-size: 0.85rem;
+    font-family: var(--font-sans);
+    cursor: pointer;
+    transition: background 0.15s;
+  }
+
+  button:hover:not(:disabled) {
+    background: var(--color-bg);
+  }
+
+  button.active {
+    background: var(--color-primary);
+    color: white;
+  }
+
+  button:disabled {
+    opacity: 0.35;
+    cursor: not-allowed;
+  }
+</style>