feat(build): embed static assets into Go binary

Embed frontend build output directly into Go binary using //go:embed.
This removes runtime dependency on ../frontend/public/ path and
simplifies Docker builds by serving assets from embedded filesystem.

- Add backend/web/embed.go with embed.FS directive
- Update server to serve from embedded static assets
- Update Makefile to copy frontend build to web/static/
- Update Dockerfile for simplified multi-stage build
- Update frontend package.json output paths
- Remove custom 'oc' command from flake.nix dev shell

flake.nix

@@ -21,11 +21,6 @@
             config.allowUnfree = true;
           }
         );
-
-        oc = pkgs.writeShellScriptBin "oc" ''
-          PRJ_ROOT=$(git rev-parse --show-toplevel 2>/dev/null || pwd)
-          cd "$PRJ_ROOT" && OPENCODE_EXPERIMENTAL_LSP_TOOL=true opencode
-        '';
       in
       {
         devShells.default = pkgs.mkShell {
@@ -38,11 +33,11 @@
             # Frontend
             bun
             watchman
-            tailwindcss_4
-
-            # Custom Commands
-            oc
           ];
+
+          shellHook = ''
+            export LD_LIBRARY_PATH=${pkgs.stdenv.cc.cc.lib}/lib:$LD_LIBRARY_PATH
+          '';
         };
       }
     );