fix(docker): apply critical patches from third-party guide

Based on https://gist.github.com/PaulMColeman/e7ef82e05035b24300d2ea1954527f10

Changes:
- Add ca-certificates for rustup HTTPS downloads
- Install Rust and WASM toolchain for frontend WebAssembly compilation
- Copy config directory needed for FLUXER_CONFIG env var
- Set FLUXER_CONFIG so rspack can derive API endpoints
- Update ENTRYPOINT to target @fluxer/server package specifically
- Fix .dockerignore to allow build scripts and locale files

These fixes address the most critical build issues documented in the
community guide for self-hosting Fluxer.

.dockerignore

@@ -38,8 +38,12 @@
 **/yarn-debug.log*
 **/yarn-error.log*
 /fluxer_app/src/data/emojis.json
-/fluxer_app/src/locales/*/messages.js
+# Don't block locale files - they're needed for the build
+#!/fluxer_app/src/locales/*/messages.js
 dev
 !fluxer_app/dist
 !fluxer_app/dist/**
 !fluxer_devops/cassandra/migrations
+# Allow build scripts and locale files
+!**/scripts/
+!**/locales/