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/about_dialog.py

@@ -0,0 +1,77 @@
+"""
+About dialog — application info, features, quick start.
+"""
+
+import customtkinter as ctk
+from version import __version__, __author__
+from core.i18n import t
+
+
+class AboutDialog(ctk.CTkToplevel):
+    def __init__(self, master):
+        super().__init__(master)
+
+        self.title(f"{t('about_title')} — {t('version')} {__version__}")
+        self.geometry("500x480")
+        self.resizable(False, False)
+        self.transient(master)
+        self.grab_set()
+
+        # ── Header ──
+        ctk.CTkLabel(
+            self, text=t("about_title"),
+            font=ctk.CTkFont(size=24, weight="bold")
+        ).pack(padx=20, pady=(25, 2))
+
+        ctk.CTkLabel(
+            self, text=f"v{__version__}",
+            font=ctk.CTkFont(size=13), text_color="#9ca3af"
+        ).pack()
+
+        ctk.CTkLabel(
+            self, text=f"by {__author__}",
+            font=ctk.CTkFont(size=11), text_color="#6b7280"
+        ).pack(pady=(0, 10))
+
+        # ── Separator ──
+        ctk.CTkFrame(self, height=1, fg_color="gray40").pack(fill="x", padx=30, pady=5)
+
+        # ── Description ──
+        ctk.CTkLabel(
+            self, text=t("about_desc"),
+            font=ctk.CTkFont(size=12), text_color="#9ca3af",
+            justify="center", wraplength=440
+        ).pack(padx=20, pady=(8, 5))
+
+        # ── Separator ──
+        ctk.CTkFrame(self, height=1, fg_color="gray40").pack(fill="x", padx=30, pady=5)
+
+        # ── Features ──
+        ctk.CTkLabel(
+            self, text=t("about_features_title"),
+            font=ctk.CTkFont(size=14, weight="bold"), anchor="w"
+        ).pack(fill="x", padx=35, pady=(8, 3))
+
+        ctk.CTkLabel(
+            self, text=t("about_features"),
+            font=ctk.CTkFont(size=12), anchor="w", justify="left"
+        ).pack(fill="x", padx=40, pady=(0, 5))
+
+        # ── Separator ──
+        ctk.CTkFrame(self, height=1, fg_color="gray40").pack(fill="x", padx=30, pady=5)
+
+        # ── Quick Start ──
+        ctk.CTkLabel(
+            self, text=t("about_howto_title"),
+            font=ctk.CTkFont(size=14, weight="bold"), anchor="w"
+        ).pack(fill="x", padx=35, pady=(8, 3))
+
+        ctk.CTkLabel(
+            self, text=t("about_howto"),
+            font=ctk.CTkFont(size=12), anchor="w", justify="left"
+        ).pack(fill="x", padx=40, pady=(0, 10))
+
+        # ── Close button ──
+        ctk.CTkButton(
+            self, text=t("close"), width=120, command=self.destroy
+        ).pack(pady=(10, 20))