fix(mcp): preserve user's enabled:false and apply disabled_mcps to all MCP sources

Commit 598a4389 refactored config-handler into separate modules but
dropped the disabledMcps parameter from loadMcpConfigs() and did not
handle the spread-order overwrite where .mcp.json MCPs (hardcoded
enabled:true) overwrote user's enabled:false from opencode.json.

Changes:
- Re-add disabledMcps parameter to loadMcpConfigs() in loader.ts
- Capture user's enabled:false MCPs before merge, restore after
- Pass disabled_mcps to loadMcpConfigs for .mcp.json filtering
- Delete disabled_mcps entries from final merged result
- Add 8 new tests covering both fixes

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

@@ -68,16 +68,24 @@ export function getSystemMcpServerNames(): Set<string> {
   return names
 }
 
-export async function loadMcpConfigs(): Promise<McpLoadResult> {
+export async function loadMcpConfigs(
+  disabledMcps: string[] = []
+): Promise<McpLoadResult> {
   const servers: McpLoadResult["servers"] = {}
   const loadedServers: LoadedMcpServer[] = []
   const paths = getMcpConfigPaths()
+  const disabledSet = new Set(disabledMcps)
 
   for (const { path, scope } of paths) {
     const config = await loadMcpConfigFile(path)
     if (!config?.mcpServers) continue
 
     for (const [name, serverConfig] of Object.entries(config.mcpServers)) {
+      if (disabledSet.has(name)) {
+        log(`Skipping MCP "${name}" (in disabled_mcps)`, { path })
+        continue
+      }
+
       if (serverConfig.disabled) {
         log(`Disabling MCP server "${name}"`, { path })
         delete servers[name]