refactor(frontend): remove MCP import functionality for v3.7.0

Auto-migration at startup is sufficient for upgrading from v3.6.x.
Manual import adds unnecessary complexity since:
- Gemini MCP support launches with v3.7.0 (no legacy data)
- Existing Claude/Codex MCP configs are auto-migrated on first run
- All MCP management should happen within CC Switch

Changes:
- Remove McpImportDialog component
- Remove "Import" button from UnifiedMcpPanel
- Remove import-related i18n translations (en/zh)
- Simplify user experience with single management interface

Note: Backend import commands (import_mcp_from_*) remain for
backward compatibility but are no longer exposed in UI.

src/i18n/locales/en.json

@@ -455,16 +455,6 @@
         "claude": "Claude",
         "codex": "Codex",
         "gemini": "Gemini"
-      },
-      "import": {
-        "title": "Import MCP Servers",
-        "button": "Import",
-        "description": "Import MCP servers from existing application configuration files. Imported servers will automatically enable the corresponding application.",
-        "fromClaudeDesc": "Import MCP servers from ~/.claude/claude.json or ~/.claude/settings.json",
-        "fromCodexDesc": "Import MCP servers from ~/.codex/config.toml",
-        "fromGeminiDesc": "Import MCP servers from Gemini configuration file",
-        "success": "Successfully imported {{count}} server(s)",
-        "noServersFound": "No servers found to import"
       }
     },
     "userLevelPath": "User-level MCP path",