chore: update default model to gpt-5.4 and remove Strix Router from docs

- Change default model from gpt-5 to gpt-5.4 across docs, tests, and examples
- Remove Strix Router references from docs, quickstart, overview, and README
- Delete models.mdx (Strix Router page) and its nav entry
- Simplify install script to suggest openai/ prefix directly
- Keep strix/ model routing support intact in code

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

strix/interface/main.py

@@ -101,7 +101,7 @@ def validate_environment() -> None:  # noqa: PLR0912, PLR0915
                 error_text.append("• ", style="white")
                 error_text.append("STRIX_LLM", style="bold cyan")
                 error_text.append(
-                    " - Model name to use with litellm (e.g., 'openai/gpt-5')\n",
+                    " - Model name to use with litellm (e.g., 'openai/gpt-5.4')\n",
                     style="white",
                 )
 
@@ -140,10 +140,7 @@ def validate_environment() -> None:  # noqa: PLR0912, PLR0915
                     )
 
         error_text.append("\nExample setup:\n", style="white")
-        if uses_strix_models:
-            error_text.append("export STRIX_LLM='strix/gpt-5'\n", style="dim white")
-        else:
-            error_text.append("export STRIX_LLM='openai/gpt-5'\n", style="dim white")
+        error_text.append("export STRIX_LLM='openai/gpt-5.4'\n", style="dim white")
 
         if missing_optional_vars:
             for var in missing_optional_vars:

strix/llm/utils.py

@@ -36,7 +36,7 @@ STRIX_MODEL_MAP: dict[str, str] = {
     "claude-opus-4.6": "anthropic/claude-opus-4-6",
     "gpt-5.2": "openai/gpt-5.2",
     "gpt-5.1": "openai/gpt-5.1",
-    "gpt-5": "openai/gpt-5",
+    "gpt-5.4": "openai/gpt-5.4",
     "gemini-3-pro-preview": "gemini/gemini-3-pro-preview",
     "gemini-3-flash-preview": "gemini/gemini-3-flash-preview",
     "glm-5": "openrouter/z-ai/glm-5",