fix(cli): add 'setup' as an alias for the install command (fixes #4112)

Discord support and other guidance still tell users 'bunx oh-my-opencode setup', but the CLI only registers 'install'. Running the recommended command produces:

  error: unknown command 'setup'

which dead-ends users who are trying to refresh missing skills (hyperplan, etc.) after upgrading. Commander.js supports first-class aliases, so declaring '.alias("setup")' on the install command makes both names route to the same action without any code duplication. Help output now reads 'Usage: oh-my-opencode install|setup [options]', which is the right discovery hint for both newcomers and users following older docs.

Regression test parses cli-program.ts and asserts the install command block contains '.alias("setup")' before its '.action(' so a future refactor of the CLI cannot silently drop the alias.

src/cli/cli-program.test.ts

@@ -0,0 +1,22 @@
+import { describe, test, expect } from "bun:test"
+import { readFile } from "node:fs/promises"
+import path from "node:path"
+
+describe("cli-program", () => {
+  test("install command exposes 'setup' as an alias so the historical install path keeps working", async () => {
+    // given
+    const cliProgramSource = await readFile(
+      path.resolve(import.meta.dir, "cli-program.ts"),
+      "utf-8",
+    )
+
+    // when
+    const installBlock = cliProgramSource.match(
+      /program\s*\n\s*\.command\("install"\)([\s\S]*?)\.action\(/,
+    )
+
+    // then
+    expect(installBlock).not.toBeNull()
+    expect(installBlock?.[1]).toContain('.alias("setup")')
+  })
+})

src/cli/cli-program.ts

@@ -24,6 +24,7 @@ program
 
 program
   .command("install")
+  .alias("setup")
   .description("Install and configure oh-my-opencode with interactive setup")
   .option("--no-tui", "Run in non-interactive mode (requires all options)")
   .option("--claude <value>", "Claude subscription: no, yes, max20")