Remove the unused crypto path and write the blob-ID hash step once (closes #151)

Production encryption and decryption already run through blobgen; the crypto package (Encryptor, Decryptor, UpdateRecipients, the fx Module) and Vaultik.GetEncryptor/GetDecryptor had no production caller. Delete crypto and route verify --deep through the same blobgen reader restore uses, parsing the age key once.

The second blob-ID hash step is now one exported blobgen.DoubleSHA256; Writer.Sum256 (the double hash) becomes Writer.ContentID so it no longer collides with Reader.Sum256 (the single plaintext hash). Also delete the never-adopted internal/types newtypes and the uncalled CleanupIncompleteSnapshots and its now-dead deleteSnapshot caller, and correct ARCHITECTURE.md. No production behavior changes.

Model: opus-4-8

internal/vaultik/vaultik.go

@@ -5,7 +5,6 @@ package vaultik
 import (
 	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -13,7 +12,6 @@ import (
 	"github.com/spf13/afero"
 	"go.uber.org/fx"
 	"sneak.berlin/go/vaultik/internal/config"
-	"sneak.berlin/go/vaultik/internal/crypto"
 	"sneak.berlin/go/vaultik/internal/database"
 	"sneak.berlin/go/vaultik/internal/globals"
 	"sneak.berlin/go/vaultik/internal/snapshot"
@@ -21,12 +19,6 @@ import (
 	"sneak.berlin/go/vaultik/internal/ui"
 )
 
-// Sentinel errors for misconfigured encryption settings.
-var (
-	errNoAgeRecipients = errors.New("no age recipients configured")
-	errNoAgeSecretKey  = errors.New("no age secret key configured")
-)
-
 // Vaultik contains all dependencies needed for vaultik operations
 type Vaultik struct {
 	Globals         *globals.Globals
@@ -141,26 +133,6 @@ func (v *Vaultik) CanDecrypt() bool {
 	return v.Config.AgeSecretKey != ""
 }
 
-// GetEncryptor creates a new Encryptor instance based on the configured age recipients
-// Returns an error if no recipients are configured
-func (v *Vaultik) GetEncryptor() (*crypto.Encryptor, error) {
-	if len(v.Config.AgeRecipients) == 0 {
-		return nil, errNoAgeRecipients
-	}
-
-	return crypto.NewEncryptor(v.Config.AgeRecipients)
-}
-
-// GetDecryptor creates a new Decryptor instance based on the configured age secret key
-// Returns an error if no secret key is configured
-func (v *Vaultik) GetDecryptor() (*crypto.Decryptor, error) {
-	if v.Config.AgeSecretKey == "" {
-		return nil, errNoAgeSecretKey
-	}
-
-	return crypto.NewDecryptor(v.Config.AgeSecretKey)
-}
-
 // GetFilesystem returns the filesystem instance used by Vaultik
 //
 //nolint:ireturn // afero.Fs is the filesystem abstraction by design