refactor: finish companion rename migration

Complete the remaining pi-to-companion rename across companion-os, web, vm-orchestrator, docker, and archived fixtures.

Verification:
- semantic rg sweeps for Pi/piConfig/getPi/.pi runtime references
- npm run check in apps/companion-os (fails in this worktree: biome not found)

Co-authored-by: Codex <noreply@openai.com>

packages/ai/src/providers/openai-codex-responses.ts

@@ -997,10 +997,10 @@ function buildHeaders(
   headers.set("Authorization", `Bearer ${token}`);
   headers.set("chatgpt-account-id", accountId);
   headers.set("OpenAI-Beta", "responses=experimental");
-  headers.set("originator", "pi");
+  headers.set("originator", "companion");
   const userAgent = _os
-    ? `pi (${_os.platform()} ${_os.release()}; ${_os.arch()})`
-    : "pi (browser)";
+    ? `companion (${_os.platform()} ${_os.release()}; ${_os.arch()})`
+    : "companion (browser)";
   headers.set("User-Agent", userAgent);
   headers.set("accept", "text/event-stream");
   headers.set("content-type", "application/json");