fix(web): make _has_env config-aware so SEARXNG_URL auto-detect honors Hermes config

Follow-up to #34306. The provider fix made SearXNG *usable* with a
config-only SEARXNG_URL, but tools/web_tools._has_env still read raw
os.getenv, so the backend auto-detect cascade and check_web_api_key
remained blind to it — SearXNG worked when explicitly selected but was
never auto-selected. Route _has_env (and the SearXNG diagnostic print)
through a config-aware _env_value helper mirroring the provider's
_searxng_url(). Fixing the shared helper covers every provider key in
one place. Adds regression tests for config-only auto-detect and
check_web_api_key. See #34290.

tools/web_tools.py

@@ -110,9 +110,28 @@ logger = logging.getLogger(__name__)
 
 # ─── Backend Selection ────────────────────────────────────────────────────────
 
+def _env_value(name: str) -> str:
+    """Resolve ``name`` via Hermes config-aware env, falling back to process env.
+
+    Mirrors the SearXNG provider's ``_searxng_url()`` so that values set
+    through Hermes' config/.env layer (``hermes config set``, ``hermes tools``)
+    are honored here too — not just raw process-env exports. Without this,
+    a config-only ``SEARXNG_URL`` (or any provider key) leaves the backend
+    auto-detect cascade and ``check_web_api_key()`` blind to it. See #34290.
+    """
+    try:
+        from hermes_cli.config import get_env_value
+
+        val = get_env_value(name)
+    except Exception:
+        val = None
+    if val is None:
+        val = os.getenv(name, "")
+    return (val or "").strip()
+
+
 def _has_env(name: str) -> bool:
-    val = os.getenv(name)
-    return bool(val and val.strip())
+    return bool(_env_value(name))
 
 def _load_web_config() -> dict:
     """Load the ``web:`` section from ~/.hermes/config.yaml."""
@@ -1204,7 +1223,7 @@ if __name__ == "__main__":
         elif backend == "tavily":
             print("   Using Tavily API (https://tavily.com)")
         elif backend == "searxng":
-            print(f"   Using SearXNG (search only): {os.getenv('SEARXNG_URL', '').strip()}")
+            print(f"   Using SearXNG (search only): {_env_value('SEARXNG_URL')}")
         elif backend == "brave-free":
             print("   Using Brave Search free tier (search only)")
         elif backend == "ddgs":