Fix production outage: build context and kiwix arg duplication

docker-compose's build context resolves relative to the symlink's own
directory (/srv/podman/maptool/), same as volume paths — but the
checkout now lives one level down in build/, so "build: ." pointed at
the wrong place and compose up --build failed outright looking for a
Dockerfile that isn't there. Point it at ./build instead.

Also drop kiwix's explicit --port=8080: the image's own start.sh
already prepends its default --port=8080 before appending the command
array, so passing it again produced "Unexpected argument" and the
container never started.

Both applied directly to production to restore service, verified via
docker-compose config + live health checks.

docker-compose.yaml

@@ -1,6 +1,16 @@
 services:
   maptool:
-    build: .
+    # "./build", not ".": the compose file's own context ("." would mean
+    # the symlink's directory, /srv/podman/maptool/ — see docs/deployment.adoc)
+    # is one level above where the actual checkout (and its Dockerfile)
+    # lives since the previous commit moved it into build/. Volume paths
+    # below resolve against that same symlink directory too, but a relative
+    # *build context* specifically needs pointing at build/ itself — the
+    # gap this fixes: production's compose up --build failed outright
+    # ("lstat .../maptool/Dockerfile: no such file or directory") until this
+    # was caught, since only the volume-path resolution got dry-run tested
+    # before the previous commit shipped, not this one.
+    build: ./build
     image: maptool:latest
     restart: unless-stopped
     ports:
@@ -72,6 +82,10 @@ services:
   kiwix:
     image: ghcr.io/kiwix/kiwix-serve:latest
     restart: unless-stopped
-    command: ["--port=8080", "/data/wikipedia.zim"]
+    # No --port here: the image's own start.sh already prepends
+    # --port=8080 (its default) before appending this command array, so
+    # passing it again produced "Unexpected argument: --port=8080,
+    # --port=8080, /data/wikipedia.zim" and kiwix-serve refused to start.
+    command: ["/data/wikipedia.zim"]
     volumes:
       - ./data/kiwix/wikipedia.zim:/data/wikipedia.zim