fix: remove build artifacts from repo, build SPA in Docker

- Remove web/dist/ from git tracking (build output)
- Add web/dist/ to .gitignore
- Add Node.js web-builder stage to Dockerfile to compile SPA at build time
- Update REPO_POLICIES.md from upstream sneak/prompts (build artifacts policy)

.gitignore

@@ -21,6 +21,7 @@ node_modules/
 *.key
 
 # Build artifacts
+web/dist/
 /neoircd
 /bin/
 *.exe