fix: use yargs built-in --no- negation for --no-oauth flag

Define `oauth` as a boolean (default `true`) so `--no-oauth` works via
yargs' built-in prefix negation instead of a custom `no-oauth` option
that conflicts with yargs' `--no-X` handling.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: suryaiyer95

packages/opencode/src/cli/cmd/mcp.ts

@@ -425,7 +425,7 @@ export const McpAddCommand = cmd({
       .option("url", { type: "string", describe: "Server URL (for remote type)" })
       .option("command", { type: "string", describe: "Command to run (for local type)" })
       .option("header", { type: "array", string: true, describe: "HTTP headers as key=value (repeatable)" })
-      .option("no-oauth", { type: "boolean", describe: "Disable OAuth" })
+      .option("oauth", { type: "boolean", describe: "Enable OAuth", default: true })
       .option("global", { type: "boolean", describe: "Add to global config", default: false }),
   async handler(args) {
     await Instance.provide({
@@ -470,7 +470,7 @@ export const McpAddCommand = cmd({
             mcpConfig = {
               type: "remote",
               url: args.url,
-              ...(args["no-oauth"] ? { oauth: false as const } : {}),
+              ...(!args.oauth ? { oauth: false as const } : {}),
               ...(Object.keys(headers).length > 0 ? { headers } : {}),
             }
           }