v1.2.0 + v1.3.0: Localization, About dialog, TOTP/2FA, stability improvements

v1.2.0:
- GUI localization (EN/RU/ZH) with language switcher and persistent selection
- About dialog (ⓘ) with app info, features, quick start guide
- core/i18n.py — internationalization module with t() function
- All GUI components translated via t() keys

v1.3.0:
- TOTP/2FA tab — Google Authenticator compatible codes with live 30s countdown,
  one-click copy, per-server secret management
- core/totp.py — TOTP module (pyotp, RFC 6238)
- core/logger.py — rotating file logger (5MB, 3 backups)
- Stronger Fernet encryption key with automatic migration from old key
- Thread-safe server store with locks, atomic writes, auto-restore on corruption
- Parallel status checks via ThreadPoolExecutor (up to 10 concurrent)
- SSH client: explicit channel cleanup, Unix key permissions
- Server dialog: port validation (1-65535), TOTP secret field
- Language change preserves active tab and server selection
- pyotp dependency added

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gui/tabs/keys_tab.py

@@ -6,6 +6,7 @@ import os
 import threading
 import customtkinter as ctk
 from core.ssh_client import SSHClientWrapper
+from core.i18n import t
 
 
 class KeysTab(ctk.CTkFrame):
@@ -15,7 +16,8 @@ class KeysTab(ctk.CTkFrame):
         self._current_alias: str | None = None
 
         # Key info
-        ctk.CTkLabel(self, text="SSH Key", font=ctk.CTkFont(size=16, weight="bold"), anchor="w").pack(fill="x", padx=15, pady=(15, 5))
+        self.key_title = ctk.CTkLabel(self, text=t("ssh_key"), font=ctk.CTkFont(size=16, weight="bold"), anchor="w")
+        self.key_title.pack(fill="x", padx=15, pady=(15, 5))
 
         self.key_path_label = ctk.CTkLabel(self, text="", anchor="w", text_color="#9ca3af")
         self.key_path_label.pack(fill="x", padx=15)
@@ -27,13 +29,13 @@ class KeysTab(ctk.CTkFrame):
         btn_frame = ctk.CTkFrame(self, fg_color="transparent")
         btn_frame.pack(fill="x", padx=15, pady=5)
 
-        self.gen_btn = ctk.CTkButton(btn_frame, text="Generate Key", command=self._generate)
+        self.gen_btn = ctk.CTkButton(btn_frame, text=t("generate_key"), command=self._generate)
         self.gen_btn.pack(side="left", padx=(0, 10))
 
-        self.install_btn = ctk.CTkButton(btn_frame, text="Install on Server", fg_color="#22c55e", hover_color="#16a34a", command=self._install)
+        self.install_btn = ctk.CTkButton(btn_frame, text=t("install_on_server"), fg_color="#22c55e", hover_color="#16a34a", command=self._install)
         self.install_btn.pack(side="left")
 
-        self.copy_btn = ctk.CTkButton(btn_frame, text="Copy Public Key", fg_color="#6b7280", command=self._copy_key)
+        self.copy_btn = ctk.CTkButton(btn_frame, text=t("copy_public_key"), fg_color="#6b7280", command=self._copy_key)
         self.copy_btn.pack(side="right")
 
         # Status log
@@ -48,7 +50,7 @@ class KeysTab(ctk.CTkFrame):
     def _refresh_key_info(self):
         key_path = self.store.get_ssh_key_path()
         pub_path = key_path + ".pub"
-        self.key_path_label.configure(text=f"Path: {key_path}")
+        self.key_path_label.configure(text=t("key_path").format(path=key_path))
 
         self.pub_key_box.configure(state="normal")
         self.pub_key_box.delete("1.0", "end")
@@ -57,10 +59,10 @@ class KeysTab(ctk.CTkFrame):
             with open(pub_path, "r") as f:
                 pub_key = f.read().strip()
             self.pub_key_box.insert("1.0", pub_key)
-            self.gen_btn.configure(state="disabled", text="Key exists")
+            self.gen_btn.configure(state="disabled", text=t("key_exists"))
         else:
-            self.pub_key_box.insert("1.0", "No key found. Click 'Generate Key' to create one.")
-            self.gen_btn.configure(state="normal", text="Generate Key")
+            self.pub_key_box.insert("1.0", t("no_key_found"))
+            self.gen_btn.configure(state="normal", text=t("generate_key"))
 
         self.pub_key_box.configure(state="disabled")
 
@@ -82,14 +84,14 @@ class KeysTab(ctk.CTkFrame):
 
     def _install(self):
         if not self._current_alias:
-            self._log("[!] No server selected")
+            self._log(t("no_server_selected"))
             return
 
         server = self.store.get_server(self._current_alias)
         if not server:
             return
 
-        self.install_btn.configure(state="disabled", text="Installing...")
+        self.install_btn.configure(state="disabled", text=t("installing"))
 
         def _do():
             try:
@@ -99,7 +101,7 @@ class KeysTab(ctk.CTkFrame):
             except Exception as e:
                 self.after(0, lambda: self._log(f"[ERROR] {e}"))
             finally:
-                self.after(0, lambda: self.install_btn.configure(state="normal", text="Install on Server"))
+                self.after(0, lambda: self.install_btn.configure(state="normal", text=t("install_on_server")))
 
         threading.Thread(target=_do, daemon=True).start()
 
@@ -111,6 +113,6 @@ class KeysTab(ctk.CTkFrame):
                 pub_key = f.read().strip()
             self.clipboard_clear()
             self.clipboard_append(pub_key)
-            self._log("Public key copied to clipboard")
+            self._log(t("key_copied"))
         else:
-            self._log("[!] No public key to copy")
+            self._log(t("no_public_key"))