Remove svgs, update puml diagrams -- separate auth diagram into multiple diagrams

docs/website/diagrams-src/auth/delete-account.puml

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+@startuml delete-account
+!include ../../../pipeline/diagrams/biergarten-weizen-theme.puml
+skinparam sequenceMessageAlign center
+skinparam maxMessageSize 200
+
+title User Authentication Flow - Delete Account
+
+actor User
+participant "API\nController" as API
+participant "MediatR pipeline\n(ValidationBehavior)" as Mediator
+box "Handler Layer" #F1F3EA
+participant "DeleteAccountHandler" as DeleteAccountHandler
+participant "UserManager<ApplicationUser>" as UserMgr
+end box
+box "Repository / Cross-slice" #DBEEDD
+participant "DapperUserStore\n(IUserStore/IUserPasswordStore/\nIUserEmailStore)" as UserStore
+end box
+database "SQL Server" as DB
+
+note over UserMgr
+  ASP.NET Core Identity's UserManager<TUser>
+  replaces the deleted AuthRepository: handlers
+  no longer issue SQL or call Argon2 directly,
+  they delegate to UserManager, which in turn
+  calls DapperUserStore (persistence) and
+  Argon2PasswordHasher (IPasswordHasher<TUser>).
+end note
+
+User -> API: DELETE /api/auth/account\n(requires Bearer access token)
+activate API
+
+API -> Mediator: Send(DeleteAccountCommand(\n  GetAuthenticatedUserId()))
+activate Mediator
+
+Mediator -> DeleteAccountHandler: Handle(command)
+activate DeleteAccountHandler
+
+DeleteAccountHandler -> UserMgr: FindByIdAsync(userAccountId)
+activate UserMgr
+UserMgr -> UserStore: FindByIdAsync(userAccountId)
+UserStore --> UserMgr: ApplicationUser or null
+UserMgr --> DeleteAccountHandler: ApplicationUser or null
+deactivate UserMgr
+
+alt Account not found
+  DeleteAccountHandler -> Mediator: throw NotFoundException
+  Mediator -> API: propagate
+  API -> User: 404 Not Found
+else Account found
+
+  DeleteAccountHandler -> UserMgr: DeleteAsync(user)
+  activate UserMgr
+  UserMgr -> UserStore: DeleteAsync(user)
+  activate UserStore
+  UserStore -> DB: DELETE FROM dbo.UserAccount\nWHERE UserAccountID = @Id
+  note right of UserStore
+    UserCredential/UserVerification/UserAvatar
+    cascade on delete. Posts, comments, photos,
+    and follows use ON DELETE NO ACTION - if any
+    reference this account, the DELETE throws a
+    foreign key violation (SQL error 547).
+  end note
+
+  alt Foreign key violation (dependent records exist)
+    UserStore --> UserMgr: IdentityResult.Failed\n(AccountHasDependentRecords)
+  else Delete succeeds
+    UserStore --> UserMgr: IdentityResult.Success
+  end
+  deactivate UserStore
+  UserMgr --> DeleteAccountHandler: IdentityResult
+  deactivate UserMgr
+
+  alt Account has dependent records
+    DeleteAccountHandler -> Mediator: throw ConflictException\n"Account cannot be deleted while it still\nhas associated posts, comments, photos,\nor follows."
+    Mediator -> API: propagate
+    API -> User: 409 Conflict
+  else !result.Succeeded (other failure)
+    DeleteAccountHandler -> Mediator: throw ConflictException
+    Mediator -> API: propagate
+    API -> User: 409 Conflict
+  else result.Succeeded
+    DeleteAccountHandler --> Mediator: (void)
+    deactivate DeleteAccountHandler
+    Mediator --> API: (void)
+    deactivate Mediator
+    API -> User: 200 OK\n{message: "Account deleted successfully."}
+  end
+end
+deactivate API
+
+@enduml