feat(mcp): add grep_app builtin MCP for ultra-fast GitHub code search

- Add grep_app MCP configuration (https://mcp.grep.app)
- Update explore agent with grep_app usage guide:
  - Always launch 5+ grep_app calls with query variations
  - Always add 2+ other search tools for verification
  - grep_app is fast but potentially outdated, use as starting point only
- Update README.md and README.ko.md with grep_app documentation

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

src/mcp/grep-app.ts

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

src/mcp/index.ts

@@ -1,5 +1,6 @@
 import { websearch_exa } from "./websearch-exa"
 import { context7 } from "./context7"
+import { grep_app } from "./grep-app"
 import type { McpName } from "./types"
 
 export { McpNameSchema, type McpName } from "./types"
@@ -7,6 +8,7 @@ export { McpNameSchema, type McpName } from "./types"
 const allBuiltinMcps: Record<McpName, { type: "remote"; url: string; enabled: boolean }> = {
   websearch_exa,
   context7,
+  grep_app,
 }
 
 export function createBuiltinMcps(disabledMcps: McpName[] = []) {

src/mcp/types.ts

@@ -1,5 +1,5 @@
 import { z } from "zod"
 
-export const McpNameSchema = z.enum(["websearch_exa", "context7"])
+export const McpNameSchema = z.enum(["websearch_exa", "context7", "grep_app"])
 
 export type McpName = z.infer<typeof McpNameSchema>