Remove deprecated Codex SDK provider

Delete codex-agent.ts/test.ts/unit.test.ts and related files.
Codex MCP is now the only Codex provider, registered for both
"codex" and "codex-mcp" provider IDs in bootstrap.ts.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/server/src/server/agent/providers/codex-agent.unit.test.ts

@@ -1,28 +0,0 @@
-import { describe, expect, it } from "vitest";
-import { promises as fs } from "node:fs";
-import path from "node:path";
-import os from "node:os";
-
-import { readLatestTurnContextModel } from "./codex-agent.js";
-
-describe("readLatestTurnContextModel", () => {
-  it("returns the most recent turn_context model from rollout", async () => {
-    const dir = await fs.mkdtemp(path.join(os.tmpdir(), "codex-rollout-"));
-    const file = path.join(dir, "rollout.jsonl");
-    const lines = [
-      JSON.stringify({ type: "session_meta", payload: { id: "thread-1" } }),
-      JSON.stringify({
-        type: "turn_context",
-        payload: { model: "gpt-5.1-codex", cwd: "/tmp" },
-      }),
-      JSON.stringify({
-        type: "turn_context",
-        payload: { model: "gpt-5.2-codex", cwd: "/tmp" },
-      }),
-    ];
-    await fs.writeFile(file, lines.join("\n"), "utf8");
-
-    const model = await readLatestTurnContextModel(file);
-    expect(model).toBe("gpt-5.2-codex");
-  });
-});