feat: add Vietnamese localization to GUI

Introduces a two-language (EN/VI) i18n system with hot-swap support.
All ~160 user-facing strings are centralised in gui/locales.py; views
retranslate in-place on language switch without restarting the app.

- gui/locales.py: new file — _EN/_VI dicts, t() lookup, set_language(),
  get_language(); assert guard ensures EN/VI key parity
- gui/app.py: switch_language(), _apply_startup_language(),
  _save_language_pref(), _rebuild_nav_labels(); language stored in
  config.json under ui.language; pipeline step headers and run_tool
  status lines translated
- gui/views/settings.py: Language dropdown card (English / Tiếng Việt)
- gui/views/dashboard.py: all strings via t(); static header widgets
  stored and retranslated in refresh()
- gui/views/mods.py: all strings via t(); _STATUS dict built at call
  time so server status labels update on language switch
- gui/views/tools.py: all strings via _translatable registry; tab names
  and segmented-button values kept in English (CTkTabview constraint)
- gui/views/logs.py: title + Copy/Clear buttons stored, retranslated
- gui/wizard.py: all 3 pages fully translated
- docs/huong-dan-su-dung.md: full Vietnamese user guide
- CLAUDE.md: documents localization architecture and constraints

gui/views/settings.py

@@ -4,6 +4,7 @@ from typing import TYPE_CHECKING
 
 import customtkinter as ctk
 
+from gui.locales import t
 from gui.views.base import BaseView
 
 if TYPE_CHECKING:
@@ -11,15 +12,15 @@ if TYPE_CHECKING:
 
 
 class SettingsView(BaseView):
-    """Appearance switcher, wizard re-opener, and current config display."""
+    """Appearance switcher, language selector, wizard re-opener, and current config display."""
 
     def build(self) -> None:
         self.grid_columnconfigure(0, weight=1)
         self.grid_rowconfigure(1, weight=1)
 
-        ctk.CTkLabel(self, text="Settings",
-                     font=ctk.CTkFont(size=22, weight="bold")).grid(
-            row=0, column=0, sticky="w", padx=24, pady=(20, 8))
+        self._title_lbl = ctk.CTkLabel(self, text=t("settings.title"),
+                                       font=ctk.CTkFont(size=22, weight="bold"))
+        self._title_lbl.grid(row=0, column=0, sticky="w", padx=24, pady=(20, 8))
 
         self._scroll = ctk.CTkScrollableFrame(self, fg_color="transparent")
         self._scroll.grid(row=1, column=0, sticky="nsew", padx=24, pady=(0, 12))
@@ -27,7 +28,8 @@ class SettingsView(BaseView):
         self._build_cards()
 
     def refresh(self) -> None:
-        # Config info may have changed (e.g. after wizard); rebuild cards.
+        # Config info and language may have changed; rebuild everything.
+        self._title_lbl.configure(text=t("settings.title"))
         for w in self._scroll.winfo_children():
             w.destroy()
         self._build_cards()
@@ -36,22 +38,21 @@ class SettingsView(BaseView):
         # ── Server & Paths ────────────────────────────────────────────────────
         c1 = ctk.CTkFrame(self._scroll)
         c1.pack(fill="x", pady=6)
-        ctk.CTkLabel(c1, text="Server & Path Configuration",
+        ctk.CTkLabel(c1, text=t("settings.server_card_title"),
                      font=ctk.CTkFont(size=14, weight="bold")).pack(
             anchor="w", padx=16, pady=(14, 3))
         ctk.CTkLabel(c1,
-                     text="Re-run the setup wizard to change your server URL, "
-                          "credentials, or Arma folder.",
+                     text=t("settings.server_card_desc"),
                      text_color="gray", wraplength=600, justify="left").pack(
             anchor="w", padx=16, pady=(0, 8))
-        ctk.CTkButton(c1, text="Open Setup Wizard", width=160,
+        ctk.CTkButton(c1, text=t("settings.wizard_btn"), width=160,
                       command=self.app.open_wizard).pack(
             anchor="e", padx=16, pady=(0, 14))
 
         # ── Appearance ────────────────────────────────────────────────────────
         c2 = ctk.CTkFrame(self._scroll)
         c2.pack(fill="x", pady=6)
-        ctk.CTkLabel(c2, text="Appearance",
+        ctk.CTkLabel(c2, text=t("settings.appearance_title"),
                      font=ctk.CTkFont(size=14, weight="bold")).pack(
             anchor="w", padx=16, pady=(14, 3))
         mode_var = ctk.StringVar(value=ctk.get_appearance_mode())
@@ -60,12 +61,28 @@ class SettingsView(BaseView):
                           command=ctk.set_appearance_mode,
                           width=140).pack(anchor="w", padx=16, pady=(0, 14))
 
+        # ── Language ──────────────────────────────────────────────────────────
+        c_lang = ctk.CTkFrame(self._scroll)
+        c_lang.pack(fill="x", pady=6)
+        ctk.CTkLabel(c_lang, text=t("settings.language_title"),
+                     font=ctk.CTkFont(size=14, weight="bold")).pack(
+            anchor="w", padx=16, pady=(14, 3))
+        from gui.locales import get_language
+        current_display = "Tiếng Việt" if get_language() == "vi" else "English"
+        ctk.CTkOptionMenu(
+            c_lang,
+            values=["English", "Tiếng Việt"],
+            variable=ctk.StringVar(value=current_display),
+            command=lambda v: self.app.switch_language("vi" if v == "Tiếng Việt" else "en"),
+            width=160,
+        ).pack(anchor="w", padx=16, pady=(0, 14))
+
         # ── Current config info ───────────────────────────────────────────────
         cfg = self.app.cfg
         if cfg:
             c3 = ctk.CTkFrame(self._scroll)
             c3.pack(fill="x", pady=6)
-            ctk.CTkLabel(c3, text="Current Configuration",
+            ctk.CTkLabel(c3, text=t("settings.config_title"),
                          font=ctk.CTkFont(size=14, weight="bold")).pack(
                 anchor="w", padx=16, pady=(14, 3))
             info = (