feat(repository): refactor query/mutation ports with capability-safe

interfaces

- refactor: split UserRepository into AuthUserRepository and
  AdminUserRepository capabilities
- refactor: split SessionRepository into AuthSessionRepository and
  repository-owned CLI/admin methods
- refactor: replace generic Repository Update/Delete with
  operation-specific params and ownership predicates
- refactor: replace CredentialRepository generic CRUD with
  passkey-specific methods
- refactor: replace FileRepository generic Create/Update/Delete with
  UploadedFileParams, DirectoryParams, and owned soft-delete
- refactor: remove repository fields from WebApp struct; repositories
  are now composition-time wiring only
- feat: add domain error kinds ErrParentNotFound, ErrParentNotDir,
  ErrDirectoryNotEmpty, ErrInvalidMove
- feat: add CredentialTypeAppPasskey constant
- feat: add testutil.SetUserAdmin for test fixture setup that bypasses
  production service ports
- test: add architecture test banning GORM Save in repository package
- test: add capability interface contract tests ensuring each service
  receives the minimal interface
- test: add blockingStorage helper for concurrent promotion tests
- test: add preserved DSN parameter test for sqliteImmediateDSN
- docs: update architecture decisions with repository write rules and
  capability separation
- docs: update roadmap to clarify atomic single-use refresh sessions
- docs: add -race test target to development docs

internal/model/errors.go

@@ -6,11 +6,15 @@ import (
 )
 
 var (
-	ErrNotFound       = errors.New("resource not found")
-	ErrDuplicate      = errors.New("resource already exists")
-	ErrUnauthorized   = errors.New("unauthorized")
-	ErrForbidden      = errors.New("forbidden")
-	ErrUploadTooLarge = errors.New("upload exceeds maximum size")
+	ErrNotFound          = errors.New("resource not found")
+	ErrDuplicate         = errors.New("resource already exists")
+	ErrUnauthorized      = errors.New("unauthorized")
+	ErrForbidden         = errors.New("forbidden")
+	ErrUploadTooLarge    = errors.New("upload exceeds maximum size")
+	ErrParentNotFound    = errors.New("parent resource not found")
+	ErrParentNotDir      = errors.New("parent resource is not a directory")
+	ErrDirectoryNotEmpty = errors.New("directory is not empty")
+	ErrInvalidMove       = errors.New("invalid file move")
 )
 
 // ErrorKind classifies domain errors without tying them to a transport.