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.

NOTES.md

@@ -87,6 +87,25 @@ If the registry requires a different format, check your Gitea container registry
 
 ## Resources
 
-- Third-party guide: https://gist.github.com/PaulMColeman/e7ef82e05035b24300d2ea1954527f10
+- **Third-party self-hosting guide**: https://gist.github.com/PaulMColeman/e7ef82e05035b24300d2ea1954527f10
+  - Documents 20 gotchas and fixes for building/deploying Fluxer
+  - Critical for successful Docker build
 - Domain: uwu.lc
 - Gitea: git.i5.wtf
+
+## Known Build Issues from Third-Party Guide
+
+The guide documents these critical Dockerfile fixes needed:
+1. ✅ Fix package path (app → app_proxy)
+2. ✅ Add Rust/WASM toolchain (frontend needs WebAssembly)
+3. ✅ Add ca-certificates (for rustup HTTPS download)
+4. ✅ Fix .dockerignore (unblock build scripts and locale files)
+5. ✅ Set FLUXER_CONFIG env var (rspack needs this)
+6. ✅ Copy config directory for build process
+7. ✅ Update ENTRYPOINT to target fluxer_server package
+
+Additional fixes that may be needed (will address if they come up):
+- Empty CDN endpoint handling (frontend code)
+- Content Security Policy adjustments
+- NATS configuration
+- LiveKit webhook configuration