fix: update Claude Code install URL to canonical domain

The previous URL (docs.anthropic.com/en/docs/claude-code/setup) returns
a 301 redirect to the new canonical URL at code.claude.com/docs/en/setup.

Closes #1432

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: fsilvaortiz

src/specify_cli/__init__.py

@@ -136,7 +136,7 @@ def _format_rate_limit_error(status_code: int, headers: httpx.Headers, url: str)
         "name": "Claude Code",
         "folder": ".claude/",
         "commands_subdir": "commands",
-        "install_url": "https://docs.anthropic.com/en/docs/claude-code/setup",
+        "install_url": "https://code.claude.com/docs/en/setup",
         "requires_cli": True,
     },
     "gemini": {