refactor(tests): replace local function copies in test_endpoint_resolver with real imports (#3359)

* refactor(tests): replace local function copies in test_endpoint_resolver with real imports

The test file carried 9 verbatim copies of src/endpoint_resolver.py functions
to avoid import-pollution concerns, but these copies are a drift hazard — PR #3343
had to update both in parallel.  Replace them with direct imports so future changes
to endpoint_resolver are automatically exercised by the test suite.

Also fixes _ollama_api_root in endpoint_resolver.py: the bare-URL Ollama case
(e.g. http://nas:11434 with empty path) was already handled correctly in the test
copy but was missing from the real function, which would return /chat instead of
/api/chat for native Ollama endpoints without an explicit /api prefix.

Closes #3351

* refactor: import _ollama_api_root from llm_core instead of duplicating it

endpoint_resolver already imports _detect_provider and _host_match from
llm_core. Add _ollama_api_root to that import and remove the local copy,
collapsing two implementations to one source of truth.

llm_core's version is a superset (also strips /api/chat|tags|generate paths),
and since normalize_base already removes those suffixes upstream the result
is identical for every input used here.

src/endpoint_resolver.py

@@ -12,7 +12,7 @@ from typing import Optional, Tuple, Dict
 from urllib.parse import urlparse, urlunparse
 
 from core.database import SessionLocal, ModelEndpoint
-from src.llm_core import _detect_provider, _host_match
+from src.llm_core import _detect_provider, _host_match, _ollama_api_root
 
 logger = logging.getLogger(__name__)
 
@@ -150,19 +150,6 @@ def _anthropic_api_root(base: str) -> str:
     return base
 
 
-def _ollama_api_root(base: str) -> str:
-    """Return the native Ollama API root, adding /api for ollama.com hosts."""
-    base = (base or "").strip().rstrip("/")
-    parsed = urlparse(base)
-    path = (parsed.path or "").rstrip("/")
-    if path.endswith("/api"):
-        return base
-    if _host_match(base, "ollama.com"):
-        root = f"{parsed.scheme}://{parsed.netloc}" if parsed.scheme and parsed.netloc else "https://ollama.com"
-        return root.rstrip("/") + "/api"
-    return base
-
-
 def build_chat_url(base: str) -> str:
     """Return the correct chat endpoint URL for a given base."""
     base = resolve_url(base)