Frontend state management and providers

[codebestia]

Write apps/web/docs/concepts-state-management.md covering AuthProvider/AuthContext/useAuth, WalletContext, ProtectedRoute and app/providers.tsx: the provider tree, what state lives where, and why there is no global store library.

Acceptance criteria:

• The provider nesting order is documented with the reason for it
• Each context's state, actions and consumers are documented
• Documents ProtectedRoute's redirect behaviour and the loading state that must be handled before it can decide
• Explains the boundary between context state, server state fetched per route, and IndexedDB-persisted state

[Essence-3]

@Essence-3 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, I have a solution to this issue and I would love to work on it.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Essence-3 to this issue.