build(learn): the server's image holds every package it resolves

The deploy of 46be9983 failed while building the server's image: the
Dockerfile copies halkyon_core since ADR 0021's step 1 (a060fbc2), but
.dockerignore still left it out of the build's context, and halkyon_llm,
which the module forwards the operator's assistants with since step 2,
was never copied at all. Nothing was switched: the instance kept running
v0.20.0's server.

CI never builds the images (its runner has no Docker, by design), so
test/deploy/images_test.dart now holds each Dockerfile to its package's
path dependencies, dev dependencies included as pub resolves them: every
one copied, kept in the narrowed workspace, and not left out by
.dockerignore. It failed on both before this fix. Built locally since:
the server's image builds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

.dockerignore

@@ -1,7 +1,7 @@
 # The Docker build context is the repository root. Nothing secret, local or bulky
 # goes into it: Learn's server's and curator's Dockerfiles copy their whole package
-# folders (and the server the module it builds on, with the module's client, which the
-# module's tests depend on).
+# folders (and the server every package it resolves, which test/deploy/images_test.dart
+# holds to its pubspecs, so none of them may be left out here).
 
 # Secrets and local state
 **/config/passwords.yaml
@@ -27,7 +27,6 @@ apps/learn/halkyon_learn_client/
 apps/learn/tool/
 apps/todo/
 packages/halkyon_app/
-packages/halkyon_core/
 packages/halkyon_interop/
 packages/halkyon_keys/
 packages/halkyon_ui/