Support custom corpus documentation templates

Mount a "custom" directory into the kalamar container, so users can
describe their own corpus in the KorAP user interface: Kalamar serves a
documentation page from there whenever it does not ship one itself, so a
doc/corpus.html.ep becomes the corpus page. Ship examples for that page,
for an optional references page, and for the corpus part of the
references page.

The directory defaults to ./custom and can be relocated with
KALAMAR_TEMPLATES.

Also allow overriding the kalamar image via KALAMAR_IMAGE, which is
needed to try this out on a Kalamar built from an unreleased version.

The references page needs the citation partial of Kalamar 0.66 or later.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Change-Id: I8d964c996c15aa1d4ea85f18be223d737ed6d528
diff --git a/compose.yaml b/compose.yaml
index 336522b..2015ba6 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -32,12 +32,15 @@
       - "example-index:/kustvakt/index"
     restart: "no"
   kalamar:
-    image: "korap/kalamar:0.65"
+    image: ${KALAMAR_IMAGE:-korap/kalamar:0.65}
     ports:
       - "64543:64543"
     environment:
       KALAMAR_API: "http://kustvakt:8089/api/"
       KALAMAR_EXPORT: ${KALAMAR_EXPORT:-true}
+    volumes:
+      # Templates describing your own corpus; see custom/README.md.
+      - ${KALAMAR_TEMPLATES:-./custom}:/kalamar/templates/custom:ro
     depends_on:
       - kustvakt
     profiles:
@@ -67,6 +70,8 @@
       KALAMAR_EXPORT: ${KALAMAR_EXPORT:-true}
     volumes:
       - ${PWD}/data/super_client_info:/kalamar/super_client_info:z
+      # Templates describing your own corpus; see custom/README.md.
+      - ${KALAMAR_TEMPLATES:-./custom}:/kalamar/templates/custom:ro
     depends_on:
       kustvakt-auth:
         condition: service_started