chore(adapter): drop redundant urlparse imports + dead ternary

Self-review follow-up to #19. Two cosmetic cleanups:

- urlparse is now imported at module-top (added in #17 alongside the
  auth-mode classification) so the two inline `from urllib.parse import
  urlparse` statements inside conditional branches are redundant.
- The log-format ternary " (custom upstream)" if base_url else "" lives
  inside `if base_url:` — base_url is unconditionally truthy there, so
  the else branch was dead code.

No behavior change. Tests still 7/7 green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

adapter.py

@@ -237,7 +237,6 @@ class ClaudeCodeAdapter(BaseAdapter):
         # "sonnet" fallback — that's correct behavior, no error.
         base_url = os.environ.get("ANTHROPIC_BASE_URL", "").strip()
         if base_url and not explicit_model:
-            from urllib.parse import urlparse
             host = urlparse(base_url).hostname or ""
             if host and host != "api.anthropic.com":
                 raise ValueError(
@@ -257,12 +256,10 @@ class ClaudeCodeAdapter(BaseAdapter):
         # adapter sent X to Y" without having to dig into the SDK
         # subprocess. Cheap diagnostic, no runtime cost.
         if base_url:
-            from urllib.parse import urlparse
             logger.info(
-                "claude-code: model=%s base_url_host=%s%s",
+                "claude-code: model=%s base_url_host=%s (custom upstream)",
                 model,
                 urlparse(base_url).hostname or "<unparseable>",
-                " (custom upstream)" if base_url else "",
             )
         else:
             logger.info("claude-code: model=%s base_url=anthropic-default", model)