Optimize Dockerfile layer caching

Move COPY priv after mix compile so ML model retraining doesn't bust
the compile cache. Create empty priv dirs before compile for
:code.priv_dir. Move algo.md after compile. Add docs/plans and
analysis outputs to .dockerignore.

.dockerignore

@@ -44,3 +44,8 @@ erl_crash.dump
 /assets/node_modules/
 /priv/static/assets/
 /priv/static/cache_manifest.json
+
+# Analysis outputs and plans (not needed in container)
+/docs/analysis_output*.txt
+/docs/plans/
+/.worktrees/

Dockerfile

@@ -59,33 +59,38 @@ RUN mix local.hex --force \
 # set build ENV
 ENV MIX_ENV="prod"
 
-# install mix dependencies
+# install mix dependencies (changes only when mix.exs/mix.lock change)
 COPY mix.exs mix.lock ./
 RUN mix deps.get --only $MIX_ENV
-RUN mkdir config
 
-# copy compile-time config files before we compile dependencies
-# to ensure any relevant config change will trigger the dependencies
-# to be re-compiled.
+# copy compile-time config before compiling deps
+RUN mkdir config
 COPY config/config.exs config/${MIX_ENV}.exs config/
 RUN mix deps.compile
 
+# install esbuild + tailwind binaries (cached until mix.exs changes)
 RUN mix assets.setup
 
-COPY priv priv
+# create priv dir so :code.priv_dir works at compile time
+# (actual contents copied after compile to avoid cache busting)
+RUN mkdir -p priv/models priv/static
 
+# copy application code and compile
 COPY lib lib
-COPY algo.md algo.md
-
-# Compile the release
 RUN mix compile
 
+# copy assets and build (JS/CSS changes don't require recompilation)
 COPY assets assets
-
-# compile assets
 RUN mix assets.deploy
 
-# Changes to config/runtime.exs don't require recompiling the code
+# copy priv contents (migrations, ML model, static files)
+# after compile so model retraining doesn't bust the compile cache
+COPY priv priv
+
+# algo.md is runtime documentation, not compiled
+COPY algo.md algo.md
+
+# runtime config doesn't require recompilation
 COPY config/runtime.exs config/
 
 COPY rel rel