feat: refactor and optimize frontend with Next.js App Router, TypeScript, and Tailwind CSS

- Complete refactoring of old frontend into Next.js App Router workspace
- Redesigned sidebar collapsing animation with absolute toggle positioning
- Resolved visual canvas bleed transitions between light/dark themes
- Added custom dark theme variant for toggle switch buttons
- Implemented full localization across Indonesian, English, Spanish, Japanese, and Chinese
- Synchronized HTML document themes to apply dark mode styles to portals/overlays

frontend/_not-found/__next._not-found.txt

@@ -0,0 +1,5 @@
+1:"$Sreact.fragment"
+2:I[39756,["/_next/static/chunks/0dbhjjzl8qfwv.js"],"default"]
+3:I[37457,["/_next/static/chunks/0dbhjjzl8qfwv.js"],"default"]
+4:[]
+0:{"rsc":["$","$1","c",{"children":[null,["$","$L2",null,{"parallelRouterKey":"children","template":["$","$L3",null,{}]}]]}],"isPartial":false,"staleTime":300,"varyParams":"$W4","buildId":"ncF6Dp_0OCMhTp1KUVnS4"}