fix(config): default service hosts to docker container names

The homelab is retiring *.schweitz.internal and will rebind host
ports to loopback; container-to-container traffic must use container
names on docker-dataplane.

- SEARXNG_HOST: http://localhost:8087 -> http://searxng:8080
  (SearXNG's internal port is 8080; 8087 was the host-published port)
- LIBRARY_DESK_HOST: http://localhost:8089 -> http://library-desk:8089
- CORE_API_HOST: http://localhost:8090 -> http://core-api:8083
  (8090 is the Scheduler's host port; Core-API serves 8083 internally,
  confirmed by the housekeeper client and test suite hitting :8083)
- scripts/test_housekeeper.sh: reach Core-API via localhost:8083
  instead of the LAN IP, which will refuse after loopback rebinding

Local development against host-published ports keeps working via .env
overrides (.env.example unchanged; localhost stays valid on the host).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/core/config.py

@@ -110,8 +110,8 @@ class Config(BaseSettings):
 
     # SearXNG Configuration
     SEARXNG_HOST: HttpUrl = Field(
-        default="http://localhost:8087",
-        description="SearXNG server URL"
+        default="http://searxng:8080",
+        description="SearXNG server URL (container name; internal port 8080)"
     )
     SEARXNG_TIMEOUT: int = Field(
         default=30,
@@ -138,8 +138,8 @@ class Config(BaseSettings):
         description="Total time budget for a librarian delegation in seconds"
     )
     LIBRARY_DESK_HOST: HttpUrl = Field(
-        default="http://localhost:8089",
-        description="Library-Desk API URL"
+        default="http://library-desk:8089",
+        description="Library-Desk API URL (container name; internal port 8089)"
     )
     LIBRARY_DESK_API_KEY: str = Field(
         default="",
@@ -152,8 +152,8 @@ class Config(BaseSettings):
 
     # Core-API Configuration (The Housekeeper backend)
     CORE_API_HOST: HttpUrl = Field(
-        default="http://localhost:8090",
-        description="Core-API URL for Home Assistant integration"
+        default="http://core-api:8083",
+        description="Core-API URL for Home Assistant integration (container name; internal port 8083)"
     )
     CORE_API_KEY: str = Field(
         default="",