style(frontend): 统一使用蓝色主题色替换原有颜色

将多个页面中的按钮、边框、图标等元素的颜色从 indigo、violet、amber 等统一替换为蓝色主题色 (#3b82f6 和 #2563eb)，以保持整个应用 UI 颜色的一致性。

knowhub/frontend/src/pages/Knowledge.tsx

@@ -354,7 +354,7 @@ export function Knowledge() {
         <div className="pt-2">
           <button 
             onClick={() => loadData()}
-            className="px-6 py-2 bg-[#444f60] text-white text-sm font-bold rounded-lg hover:bg-[#2c3441] shadow-md shadow-slate-200 hover:-translate-y-0.5 hover:shadow-lg transition-all"
+            className="px-6 py-2 bg-[#3b82f6] text-white text-sm font-bold rounded-lg hover:bg-[#2563eb] shadow-md shadow-slate-200 hover:-translate-y-0.5 hover:shadow-lg transition-all"
           >
             应用筛选
           </button>

knowhub/frontend/src/pages/Tools.tsx

@@ -9,7 +9,7 @@ import { cn } from '../lib/utils';
 function KnowledgeItem({ label, content }: any) {
   const [open, setOpen] = useState(false);
   return (
-    <div className="bg-white border border-slate-200 rounded-xl overflow-hidden shadow-sm hover:border-indigo-300 transition-colors">
+    <div className="bg-white border border-slate-200 rounded-xl overflow-hidden shadow-sm hover:border-[#3b82f6] transition-colors">
       <div 
         className="flex items-center gap-2 text-[12px] text-slate-700 font-bold p-2.5 cursor-pointer hover:bg-slate-50 transition-colors"
         onClick={() => setOpen(!open)}
@@ -105,10 +105,10 @@ function ToolDetails({ tool, allKnow, allCaps, onClose }: { tool: any, allKnow:
 
         <div className="pt-4 border-t border-slate-100 mt-4">
           <h3 className="font-bold text-slate-800 mb-4 text-sm flex items-center gap-2">
-            <FileText size={16} className="text-violet-600" /> 沉淀知识图谱
+            <FileText size={16} className="text-[#3b82f6]" /> 沉淀知识图谱
           </h3>
           <div className="bg-slate-50 p-4 rounded-2xl border border-slate-200">
-             {renderExpandableKnowledgeList("关联知识", tool.knowledge_ids, "text-indigo-700")}
+             {renderExpandableKnowledgeList("关联知识", tool.knowledge_ids, "text-[#3b82f6]")}
 
              {!(tool.knowledge_ids?.length) && (
                 <p className="text-xs text-slate-400 my-2">该工具暂未挂载知识点数据。</p>
@@ -209,9 +209,9 @@ export function Tools() {
              value={searchInput}
              onChange={e => setSearchInput(e.target.value)}
              placeholder="搜索特定功能点或参数设计..."
-             className="w-full bg-slate-50 border border-slate-200 text-sm rounded-xl pl-10 pr-24 py-2.5 focus:outline-none focus:ring-2 focus:ring-amber-500 transition-all font-medium text-slate-700 placeholder:font-normal"
+             className="w-full bg-slate-50 border border-slate-200 text-sm rounded-xl pl-10 pr-24 py-2.5 focus:outline-none focus:ring-2 focus:ring-[#3b82f6] transition-all font-medium text-slate-700 placeholder:font-normal"
            />
-           <button type="submit" className="absolute right-2 top-1/2 -translate-y-1/2 bg-[#3b82f6] text-white text-xs px-3 py-1.5 rounded-lg font-bold hover:bg-amber-700 transition-colors">
+           <button type="submit" className="absolute right-2 top-1/2 -translate-y-1/2 bg-[#3b82f6] text-white text-xs px-3 py-1.5 rounded-lg font-bold hover:bg-[#2563eb] transition-colors">
              检索
            </button>
         </form>

knowhub/frontend/src/pages/Workflows.tsx

@@ -201,7 +201,7 @@ export function Workflows() {
              value={searchQuery}
              onChange={e => setSearchQuery(e.target.value)}
              placeholder="模糊匹配工序名称或描述..."
-             className="w-full bg-slate-50 border border-slate-200 text-sm rounded-xl pl-10 pr-4 py-2.5 focus:outline-none focus:ring-2 focus:ring-indigo-500 transition-all font-medium text-slate-700 placeholder:font-normal"
+             className="w-full bg-slate-50 border border-slate-200 text-sm rounded-xl pl-10 pr-4 py-2.5 focus:outline-none focus:ring-2 focus:ring-[#3b82f6] transition-all font-medium text-slate-700 placeholder:font-normal"
            />
         </div>
       </div>
@@ -209,7 +209,7 @@ export function Workflows() {
       <div className="space-y-6">
         {isLoading && (
            <div className="p-12 text-center text-slate-400 font-bold flex flex-col items-center gap-3">
-               <div className="w-8 h-8 border-4 border-indigo-200 border-t-indigo-600 rounded-full animate-spin"></div>
+               <div className="w-8 h-8 border-4 border-indigo-200 border-t-[#3b82f6] rounded-full animate-spin"></div>
                正在加载工序网...
            </div>
         )}
@@ -269,7 +269,7 @@ export function Workflows() {
                        return (
                          <div className="mt-4 border border-slate-100 rounded-xl overflow-hidden bg-slate-50/50">
                            <div className="px-4 py-2 bg-slate-100/50 border-b border-slate-100 text-[11px] font-bold text-slate-500 uppercase tracking-wider flex items-center gap-2">
-                              <Target size={14} className="text-indigo-400" />
+                              <Target size={14} className="text-[#3b82f6]" />
                               覆盖需求判定
                            </div>
                            <div className="divide-y divide-slate-100">
@@ -410,7 +410,7 @@ export function Workflows() {
                                       const cap = capabilities[capIdStr] || (typeof capObj === 'object' ? capObj : null);
                                       const capName = cap?.capability_name || cap?.name || capObj?.capability_name || capObj?.name || capIdStr;
                                       return (
-                                        <span key={i} className="px-2 py-1 bg-indigo-50 text-indigo-600 rounded text-xs font-bold whitespace-nowrap">
+                                        <span key={i} className="px-2 py-1 bg-indigo-50 text-[#3b82f6] rounded text-xs font-bold whitespace-nowrap">
                                           {capName}
                                         </span>
                                       );