docs: update ARCHITECTURE.md to document implemented Supabase cloud sync

[phoneuooyd]

Motivation

• Document the existing and recently-enabled local-first Supabase synchronization so architecture docs match the codebase (models, migrations and runtime config).
• Clarify dataflow, security and operational scenarios so engineers have a single reference for sync behaviour, local persistence and conflict handling.

Description

• Added a dedicated "Cloud Sync / Supabase" section describing components/models AuthAccount, SyncState, and SyncQueueEntry, and referencing DTOs in Models/DTOs such as PlanDto, RecipeDto, IngredientDto, and ShoppingListItemDto.
• Updated the Data layer to document local sync persistence (SyncQueue, SyncStates, AuthAccounts) and noted active EF Migrations in Data/Migrations (e.g. 20260126193304_InitialCreate).
• Documented runtime configuration from FoodbookApp.App/Properties/appsettings.json (Supabase section and Authentication JWT settings), the local-first sync flow (SQLite → queue → Supabase → SyncState updates + retry handling), and a security subsection covering token handling, data minimization, risks and mitigations.
• Added operational scenarios (first sync, force sync, conflict resolution strategy, offline/online behaviour) and updated ADRs/roadmap to mark Supabase sync as implemented / actively developed.

Testing

• Verified presence of models and DTOs with repository searches (e.g. rg --files / rg), and confirmed AuthAccount, SyncQueue and SyncStates model files exist prior to doc change.
• Confirmed runtime settings by reading FoodbookApp.App/Properties/appsettings.json with cat and validated EF migration files in FoodbookApp.App/Data/Migrations with rg.
• Inspected and reviewed the updated document content using nl -ba FoodbookApp.App/DOCS/ARCHITECTURE.md | sed -n '1,260p' and git diff -- FoodbookApp.App/DOCS/ARCHITECTURE.md; all inspection checks completed successfully.

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Codex Task

[phoneuooyd]

ok