feat(codex): declare gpt-5.6 context window for Claude Code takeover

- Update Codex OAuth presets to the gpt-5.6 family (haiku -> gpt-5.6-luna)
  and bump the custom Codex template default model
- Inject CLAUDE_CODE_MAX_CONTEXT_TOKENS / CLAUDE_CODE_AUTO_COMPACT_WINDOW
  (372000, the ChatGPT Codex catalog window with a ~353K effective budget,
  openai/codex#31860) into effective live settings so Claude Code stops
  assuming a 200K window and compacts before the upstream rejects the prompt
- Gate the injected defaults on every configured model being gpt-5.6*:
  gpt-5.5's upstream catalog oscillates between 272K and 372K and must not
  inherit them; explicit user values always win
- Strip the injected values on switch-away backfill (mirror-inverse of the
  injection conditions) so program defaults never harden into per-provider
  explicit values, and keep both keys out of the shared common-config snippet

src/config/claudeDesktopProviderPresets.ts

@@ -394,7 +394,7 @@ export const claudeDesktopProviderPresets: ClaudeDesktopProviderPreset[] = [
     apiFormat: "openai_responses",
     providerType: "codex_oauth",
     requiresOAuth: true,
-    modelRoutes: brandedRoutes("gpt-5.5", "gpt-5.5", "gpt-5.4-mini"),
+    modelRoutes: brandedRoutes("gpt-5.6", "gpt-5.6", "gpt-5.6-luna"),
     icon: "openai",
     iconColor: "#000000",
   },