Rename apps to interfaces, when outside of modules folder

[jravenel]

Current State:

• Unclear distinction between interfaces and module-specific apps
• APIs not explicitly integrated into our interface design, it's outside of core/custom

Target State:

We need to establish a clear hierarchy and nomenclature:

Interfaces:
Located in src/core/interfaces
Abstract definitions that can load and interact with both core and custom modules
Examples: DashInterface, StreamlitInterface, PlotlyInterface, even API and CLI could go there (they are now outside of the folders)

Module-Specific Apps:
Located in src/core/modules/<module_name>/apps
Concrete apps implementations specific to a particular module

src/
├── core/
│ ├── interfaces/
│ │ ├── dash_interface.py
│ │ ├── streamlit_interface.py
│ │ └── plotly_interface.py
│ │ └── api.py
│ └── modules/
│ ├── data_analysis/
│ │ └── apps/
│ │ └── data_viz_app.py
│ ├── nlp/
│ │ └── apps/
│ │ └── text_processor_app.py
│ └── main/
│ └── apps/
│ └── main_app.py

[jravenel]

@Dr0p42 what do you think??