feat(claude-code-mcp-loader): auto-disable builtin skills with overlapping MCP servers

Add getSystemMcpServerNames() sync function to detect system-configured MCP
servers from .mcp.json files (user, project, and local scopes). Builtin skills
like playwright are now automatically excluded when their MCP server is already
configured in system config, preventing duplicate MCP server registration.

Also adds comprehensive test suite with 5 BDD-style tests covering empty config,
project/local scopes, disabled servers, and merged configurations.

Changes:
- loader.ts: Add getSystemMcpServerNames() function + readFileSync import
- loader.test.ts: Add 5 tests for getSystemMcpServerNames() edge cases
- index.ts: Filter builtin skills to exclude those with overlapping MCP names

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/features/claude-code-mcp-loader/loader.ts

@@ -1,4 +1,4 @@
-import { existsSync } from "fs"
+import { existsSync, readFileSync } from "fs"
 import { join } from "path"
 import { getClaudeConfigDir } from "../../shared"
 import type {
@@ -42,6 +42,30 @@ async function loadMcpConfigFile(
   }
 }
 
+export function getSystemMcpServerNames(): Set<string> {
+  const names = new Set<string>()
+  const paths = getMcpConfigPaths()
+
+  for (const { path } of paths) {
+    if (!existsSync(path)) continue
+
+    try {
+      const content = readFileSync(path, "utf-8")
+      const config = JSON.parse(content) as ClaudeCodeMcpConfig
+      if (!config?.mcpServers) continue
+
+      for (const [name, serverConfig] of Object.entries(config.mcpServers)) {
+        if (serverConfig.disabled) continue
+        names.add(name)
+      }
+    } catch {
+      continue
+    }
+  }
+
+  return names
+}
+
 export async function loadMcpConfigs(): Promise<McpLoadResult> {
   const servers: McpLoadResult["servers"] = {}
   const loadedServers: LoadedMcpServer[] = []