feat: add S/MIME store for managing key records and public certificates

- Implemented Zustand store for S/MIME functionality, including state management for key records and public certificates.
- Added methods for importing PKCS#12 files and public certificates, binding identities to keys, and managing unlocked keys.
- Introduced session storage for remembering unlocked keys across sessions.
- Enhanced error handling and loading states during data operations.

locales/en/common.json

@@ -421,7 +421,16 @@
     "continue_draft": "Continue draft",
     "close_draft_title": "Save or discard draft?",
     "close_draft_message": "You have unsaved changes. Would you like to save this as a draft or discard it?",
-    "save_draft": "Save Draft"
+    "save_draft": "Save Draft",
+    "smime_sign_on": "S/MIME signing enabled",
+    "smime_sign_off": "Enable S/MIME signing",
+    "smime_encrypt_on": "S/MIME encryption enabled",
+    "smime_encrypt_off": "Enable S/MIME encryption",
+    "smime_encrypt_unavailable": "S/MIME encryption unavailable – missing recipient certificates",
+    "smime_unlock_title": "Unlock S/MIME Key",
+    "smime_unlock_message": "Enter the passphrase to unlock your S/MIME signing key.",
+    "smime_unlock_button": "Unlock",
+    "smime_passphrase_placeholder": "Passphrase"
   },
   "confirm_dialog": {
     "confirm": "Confirm",
@@ -553,7 +562,8 @@
       "keywords": "Keywords",
       "security": "Security",
       "files": "Files",
-      "contacts": "Contacts"
+      "contacts": "Contacts",
+      "encryption": "Encryption"
     },
     "tab_groups": {
       "general": "General",
@@ -1412,6 +1422,15 @@
       "categories": "Categories",
       "related_contacts": "Related Contacts",
       "crypto_keys": "Crypto Keys",
+      "cert_issuer": "Issuer",
+      "cert_expires": "Expires",
+      "cert_expired": "Expired",
+      "cert_fingerprint": "Fingerprint",
+      "cert_algorithm": "Algorithm",
+      "import_to_smime": "Import to S/MIME",
+      "cert_already_imported": "Already imported to S/MIME",
+      "cert_imported": "Certificate imported to S/MIME store",
+      "cert_import_failed": "Failed to import certificate",
       "no_contact_selected": "Select a contact to view details",
       "compose_email": "Compose email",
       "copy_email": "Copy email",
@@ -1989,5 +2008,82 @@
     "settings_folder_layout_desc": "Choose how folders are displayed: inline with files or in a sidebar tree",
     "settings_folder_layout_inline": "Inline",
     "settings_folder_layout_sidebar": "Sidebar"
+  },
+  "smime": {
+    "your_certificates": "Your Certificates",
+    "your_certificates_desc": "Import and manage your S/MIME certificates for signing and encrypting emails",
+    "recipient_certificates": "Recipient Certificates",
+    "recipient_certificates_desc": "Public certificates for encrypting emails to recipients",
+    "identity_bindings": "Identity Key Bindings",
+    "identity_bindings_desc": "Bind S/MIME certificates to your email identities",
+    "defaults_title": "Defaults",
+    "defaults_desc": "Configure default signing and encryption behavior",
+    "import_pkcs12": "Import PKCS#12 (.p12/.pfx)",
+    "import_public_cert": "Import Certificate",
+    "no_certificates": "No certificates imported yet",
+    "no_recipient_certs": "No recipient certificates",
+    "expires": "Expires",
+    "expired": "Expired",
+    "bound_to": "Bound to",
+    "no_key_bound": "None",
+    "lock": "Lock key",
+    "unlock": "Unlock key",
+    "details": "View details",
+    "delete": "Delete",
+    "encrypt_by_default": "Encrypt by default",
+    "encrypt_by_default_desc": "Automatically encrypt emails when all recipients have certificates",
+    "remember_unlocked": "Remember unlocked keys",
+    "remember_unlocked_desc": "Keep keys unlocked for the duration of this browser session",
+    "sign_default_for": "Sign by default for",
+    "enter_p12_passphrase": "Enter PKCS#12 Passphrase",
+    "p12_passphrase_desc": "Enter the passphrase that protects this certificate file",
+    "enter_storage_passphrase": "Set Storage Passphrase",
+    "storage_passphrase_desc": "Choose a passphrase to protect this key at rest in your browser",
+    "next": "Next",
+    "import": "Import",
+    "unlock_key": "Unlock Key",
+    "unlock_key_desc": "Enter the storage passphrase to unlock this key for signing or decryption",
+    "passphrase_placeholder": "Enter passphrase",
+    "confirm_passphrase_placeholder": "Confirm passphrase",
+    "passphrase_mismatch": "Passphrases do not match",
+    "cancel": "Cancel",
+    "processing": "Processing…",
+    "close": "Close",
+    "certificate_details": "Certificate Details",
+    "cert_subject": "Subject",
+    "cert_issuer": "Issuer",
+    "cert_email": "Email",
+    "cert_serial": "Serial Number",
+    "cert_validity": "Validity",
+    "cert_fingerprint": "Fingerprint (SHA-256)",
+    "cert_algorithm": "Algorithm",
+    "cert_capabilities": "Capabilities",
+    "cert_source": "Source",
+    "cert_expired": "This certificate has expired",
+    "cert_not_yet_valid": "This certificate is not yet valid",
+    "cap_sign": "Signing",
+    "cap_encrypt": "Encryption",
+    "cap_none": "None",
+    "show_passphrase": "Show passphrase",
+    "hide_passphrase": "Hide passphrase",
+    "sign_toggle": "Sign",
+    "encrypt_toggle": "Encrypt",
+    "missing_recipient_certs": "Missing certificates for: {emails}",
+    "missing_sender_cert": "No certificate bound to this identity",
+    "status_encrypted_ok": "This message was encrypted",
+    "status_encrypted_no_key": "This message is encrypted but no matching key was found",
+    "status_encrypted_failed": "Failed to decrypt this message",
+    "status_signed_valid": "Signature verified",
+    "status_signed_invalid": "Signature verification failed",
+    "status_signed_expired_cert": "Signed with an expired certificate",
+    "status_signed_mismatch": "Signature valid, but signer does not match sender",
+    "status_unsupported": "Unsupported S/MIME format",
+    "auto_import_signer_certs": "Auto-import signer certificates",
+    "auto_import_signer_certs_desc": "Automatically save certificates from verified signed emails for future encryption",
+    "export": "Export",
+    "enter_export_passphrase": "Set Export Passphrase",
+    "export_passphrase_desc": "Choose a passphrase to protect the exported PKCS#12 file",
+    "export_storage_desc": "Enter the storage passphrase to decrypt the key for export",
+    "incorrect_passphrase": "Incorrect passphrase"
   }
 }