feat(model): add GPT-5.5 support for Codex provider (#880)

- Bump Codex provider defaults from gpt-5.4 to gpt-5.5 across all ModelConfigs
- Update codexplan alias to resolve to gpt-5.5
- Add gpt-5.5 and gpt-5.5-mini to model picker with reasoning effort mappings
- Add context window and max output token specs for gpt-5.5 family
- Add gpt-5.5 entries to COPILOT_MODELS registry
- Keep official OpenAI API preset at gpt-5.4 (API availability pending)
- Update codexShim tests to expect gpt-5.5 from codexplan alias

Co-authored-by: OpenClaude <openclaude@gitlawb.com>

src/utils/providerProfiles.ts

@@ -153,7 +153,7 @@ export function getProviderPresetDefaults(
         provider: 'openai',
         name: 'OpenAI',
         baseUrl: 'https://api.openai.com/v1',
-        model: 'gpt-5.3-codex',
+        model: 'gpt-5.4',
         apiKey: '',
         requiresApiKey: true,
       }