fix(mcp): unify header buttons style with skills panel

Changed MCP panel buttons to match Skills panel styling:
- Replace circular orange icon button with ghost text button
- Update button labels: "Import" → "Import Existing", add "Add MCP"

src/i18n/locales/en.json

@@ -566,6 +566,8 @@
   "mcp": {
     "title": "MCP Management",
     "import": "Import",
+    "importExisting": "Import Existing",
+    "addMcp": "Add MCP",
     "claudeTitle": "Claude Code MCP Management",
     "codexTitle": "Codex MCP Management",
     "geminiTitle": "Gemini MCP Management",

src/i18n/locales/ja.json

@@ -566,6 +566,8 @@
   "mcp": {
     "title": "MCP 管理",
     "import": "インポート",
+    "importExisting": "既存をインポート",
+    "addMcp": "MCPを追加",
     "claudeTitle": "Claude Code MCP 管理",
     "codexTitle": "Codex MCP 管理",
     "geminiTitle": "Gemini MCP 管理",

src/i18n/locales/zh.json

@@ -566,6 +566,8 @@
   "mcp": {
     "title": "MCP 管理",
     "import": "导入",
+    "importExisting": "导入已有",
+    "addMcp": "添加MCP",
     "claudeTitle": "Claude Code MCP 管理",
     "codexTitle": "Codex MCP 管理",
     "geminiTitle": "Gemini MCP 管理",