Refactor LLM API key handling for Ollama

The LLM client now conditionally adds the `Authorization` header only
when an API key is provided. The `llm_configured` check is updated to
reflect that an API key is not strictly required for Ollama-style
endpoints. A new integration test verifies the functionality against an
Ollama-compatible endpoint without an API key.

server/src/config.rs

@@ -105,11 +105,14 @@ impl Config {
         }
     }
 
-    /// True iff all three required fields for the external analysis LLM are
-    /// non-empty. Used to gate the "Fall abschließen" UI and handler — if
-    /// no LLM is configured, the close action must not be reachable.
+    /// True iff the external analysis LLM is configured. `llm_api_key` is
+    /// intentionally **not** required — Ollama's OpenAI-compatible endpoint
+    /// at `/v1/chat/completions` accepts unauthenticated requests and is a
+    /// supported deployment target. For hosted providers (Ionos, OpenAI) the
+    /// key remains necessary in practice; the provider will reject with 401
+    /// if it is missing, which is correct feedback.
     pub fn llm_configured(&self) -> bool {
-        !self.llm_url.is_empty() && !self.llm_api_key.is_empty() && !self.llm_model.is_empty()
+        !self.llm_url.is_empty() && !self.llm_model.is_empty()
     }
 
     /// Sane defaults for integration tests. Not a `Default` impl on purpose: