feat(mcp): add context7 MCP and disabled_mcps config support

- Add context7 MCP for library documentation lookup
- Add oh-my-opencode.json config file support for per-project settings
- Support disabled_mcps array to selectively disable built-in MCPs
- Update documentation with Configuration section

src/mcp/context7.ts

@@ -0,0 +1,5 @@
+export const context7 = {
+  type: "remote" as const,
+  url: "https://mcp.context7.com/mcp",
+  enabled: true,
+}

src/mcp/index.ts

@@ -1,5 +1,23 @@
 import { websearch_exa } from "./websearch-exa"
+import { context7 } from "./context7"
 
-export const builtinMcps = {
+export type McpName = "websearch_exa" | "context7"
+
+const allBuiltinMcps: Record<McpName, { type: "remote"; url: string; enabled: boolean }> = {
   websearch_exa,
+  context7,
 }
+
+export function createBuiltinMcps(disabledMcps: McpName[] = []) {
+  const mcps: Record<string, { type: "remote"; url: string; enabled: boolean }> = {}
+
+  for (const [name, config] of Object.entries(allBuiltinMcps)) {
+    if (!disabledMcps.includes(name as McpName)) {
+      mcps[name] = config
+    }
+  }
+
+  return mcps
+}
+
+export const builtinMcps = allBuiltinMcps