Revamp app architecture

Revamp the old app architecture as discussed:
- [ ] Add riverpod state management.
- [ ] Fix the folder structure
- [ ] Decrease the over-modularization by bringing related widgets in the same file. (Unless they're share a lot of places or are very big)

Start by reviewing the current app architecture and folder structure against the three checklist items in this issue. Identify how state management, widget placement, and module boundaries are currently organized before proposing changes. Done means Riverpod is integrated, the folder structure is revised, and over-modularized related widgets are consolidated without disrupting shared or large components.

Written by the indexing model from the issue text.