Refactor AppModels according to refined API spec

[Arlodotexe]

Related to #4

Refactor AppModels to align with the refined API specification.

• Add IReadOnlyEntity interface with common properties and events.
• Add IModifiableEntity interface with common methods for updating properties.
• Modify IReadOnlyUser to inherit from IReadOnlyEntity, remove MarkdownAboutMe and Icon properties, add ExtendedDescription property, and add methods for retrieving publishers and projects along with their roles.
• Modify IModifiableUser to inherit from IModifiableEntity, remove UpdateMarkdownAboutMeAsync and UpdateIconAsync methods, and add methods for adding/removing publishers and projects along with their roles.
• Modify IReadOnlyPublisher to inherit from IReadOnlyEntity, remove Owner, ContactEmail, and Icon properties, add ExtendedDescription and ForgetMe properties, add methods for retrieving users along with their roles, and add properties for Connections and Links.
• Modify IModifiablePublisher to inherit from IModifiableEntity, remove UpdateOwnerAsync and UpdateIconAsync methods, add methods for adding/removing users along with their roles, and add methods for adding/removing connections and links.
• Modify IReadOnlyProject to inherit from IReadOnlyEntity, remove HeroImage, CreatedAt, and Icon properties, add ExtendedDescription property, and replace Cid and DagCid with IReadOnlyConnection.
• Modify IModifiableProject to inherit from IModifiableEntity, remove UpdateHeroImageAsync and UpdateIconAsync methods, add methods for adding/removing connections, and replace Cid and DagCid with IReadOnlyConnection.
• Add IReadOnlyConnection interface with properties Key and Value, and event handlers for ValueChanged.
• Add IModifiableConnection interface with methods for updating Key and Value.

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[Arlodotexe]

Hit quota before I could finish, still needs:

Create common interfaces (one read-only, one modifiable) for collections of IReadOnlyConnection

Will do the remaining work offline.