build(docker): trim build context, fix docs/ ignore typo

The .dockerignore excluded a non-existent doc/ directory (the real one is
docs/) and did not exclude tests/, images/, charts/, or tools/. None of
these are COPYed by the Dockerfile, yet ~24 MB of them were sent to the
daemon as build context on every build. Fix the typo and exclude the
unused asset/tooling directories so the context stays minimal.

https://claude.ai/code/session_01GpprjxjtXFYLfXNkoKnHuL

.dockerignore

@@ -21,11 +21,19 @@ rootless-compose.yml
 storage/
 
 # Documentation
-doc/
+docs/
 *.md
 LICENSE
 CODEOWNERS
 
+# Project assets and tooling not needed by the build
+# (the Dockerfile only COPYs src, static, migrations, templates, build.rs,
+#  Cargo.*, and entrypoint.sh; everything else is dead weight in the context)
+images/
+charts/
+tools/
+tests/
+
 # Miscellaneous
 .github/
 .env