style: 优化后台页面 slug 生成按钮样式

src/routes/admin/categories/+page.svelte

@@ -61,8 +61,7 @@
 					<label for="slug" style="margin: 0;">别名</label>
 					<button
 						type="button"
-						class="btn btn-secondary"
-						style="padding: 0.2rem 0.6rem; font-size: 0.8rem; cursor: pointer; flex-shrink: 0; min-width: max-content;"
+						style="background: none; border: none; padding: 0; color: #666; font-size: 0.8rem; cursor: pointer; outline: none;"
 						onclick={() => slugHandler.forceGenerate(name)}
 						disabled={isGenerating}
 					>

src/routes/admin/pages/new/+page.svelte

@@ -108,8 +108,7 @@
 					<h3 style="margin: 0;">别名 *</h3>
 					<button
 						type="button"
-						class="btn btn-secondary"
-						style="padding: 0.2rem 0.6rem; font-size: 0.8rem; cursor: pointer; flex-shrink: 0; min-width: max-content;"
+						style="background: none; border: none; padding: 0; color: #666; font-size: 0.8rem; cursor: pointer; outline: none;"
 						onclick={() => slugHandler.forceGenerate(title)}
 						disabled={isGenerating}
 					>

src/routes/admin/posts/new/+page.svelte

@@ -518,8 +518,7 @@
 					<h3 style="margin: 0;">别名 *</h3>
 					<button
 						type="button"
-						class="btn btn-secondary"
-						style="padding: 0.2rem 0.6rem; font-size: 0.8rem; cursor: pointer; flex-shrink: 0; min-width: max-content;"
+						style="background: none; border: none; padding: 0; color: #666; font-size: 0.8rem; cursor: pointer; outline: none;"
 						title="生成英文 Slug"
 						onclick={() => slugHandler.forceGenerate(title)}
 						disabled={isGenerating}

src/routes/admin/series/+page.svelte

@@ -55,8 +55,7 @@
 				<label for="slug" style="margin: 0;">URL 别名 *</label>
 				<button
 					type="button"
-					class="btn btn-secondary"
-					style="padding: 0.2rem 0.6rem; font-size: 0.8rem; cursor: pointer; flex-shrink: 0; min-width: max-content;"
+					style="background: none; border: none; padding: 0; color: #666; font-size: 0.8rem; cursor: pointer; outline: none;"
 					onclick={() => slugHandler.forceGenerate(name)}
 					disabled={isGenerating}
 				>