[OSS-129] Map GPT-5.6 family to the official 1.05M context window (#7012)

* fix(core): map GPT-5.6 to the official 1.05M context window

LiteLLM fallback treated Sol, Terra, Luna, and the gpt-5.6 alias as unknown and used the 8k default.

* fix(openai): give GPT-5.6 its own 1.05M window

Native lookup matched gpt-5 first, so Sol, Terra, and Luna inherited 1,047,576. Longest-prefix matching keeps gpt-5 and gpt-5.4-mini on their own sizes.

* fix(azure): map GPT-5.6 deployments to the official 1.05M window

Azure had no gpt-5 / gpt-5.6 entry, so Sol, Terra, and Luna fell back to 8k.

* feat(cli): list GPT-5.6 Sol, Terra, and Luna in curated catalogs

The family is generally available; keep gpt-5.5 as the offline default.

* refactor: keep context-window tables in longest-prefix order

Drop the runtime sort and document that new keys must be inserted longest-first so startswith matching stays correct.

* fix(core): resolve prefixed LiteLLM models to the GPT-5.6 window

openai/gpt-5.6-luna kept its provider prefix on self.model, so startswith matching missed the 1.05M mapping. Strip recognized prefixes for lookup and leave unknown ones intact.

lib/cli/tests/test_constants.py

@@ -18,3 +18,10 @@ def test_huggingface_models():
     """Test that Huggingface models are properly configured."""
     assert "huggingface" in MODELS
     assert len(MODELS["huggingface"]) > 0
+
+
+def test_openai_models_include_gpt56_family() -> None:
+    """Curated OpenAI list should include Sol, Terra, Luna, and the alias."""
+    openai_models = MODELS["openai"]
+    for model in ("gpt-5.6-sol", "gpt-5.6-terra", "gpt-5.6-luna", "gpt-5.6"):
+        assert model in openai_models