Add CS2 pattern fetcher subtool

Introduce a CS2 pattern download tool with toolbar entry, translations, and requests dependency. Document the workflow and requirements updates.

app/gui/ui.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 import colorsys
 import tkinter as tk
 import tkinter.font as tkfont
-from tkinter import ttk
+from tkinter import messagebox, ttk
 
 
 class UIBuilderMixin:
@@ -24,6 +24,7 @@ class UIBuilderMixin:
             ("💾", self._t("toolbar.save_overlay"), self.save_overlay),
             ("△", self._t("toolbar.toggle_free_draw"), self.toggle_exclusion_mode),
             ("🧹", self._t("toolbar.clear_excludes"), self.clear_excludes),
+            ("🎯", self._t("toolbar.cs2_tool"), self.open_cs2_pattern_tool),
             ("↩", self._t("toolbar.undo_exclude"), self.undo_exclude),
             ("🔄", self._t("toolbar.reset_sliders"), self.reset_sliders),
             ("🌓", self._t("toolbar.toggle_theme"), self.toggle_theme),
@@ -522,6 +523,18 @@ class UIBuilderMixin:
                 activeforeground=palette["fg"],
             )
 
+    def open_cs2_pattern_tool(self) -> None:
+        try:
+            from app.tools import open_cs2_pattern_tool as _open_cs2_pattern_tool
+        except Exception as exc:  # noqa: BLE001
+            messagebox.showerror(
+                self._t("dialog.error_title"),
+                self._t("cs2.launch_error").format(error=str(exc)),
+                parent=getattr(self, "root", None),
+            )
+            return
+        _open_cs2_pattern_tool(self)
+
     def _canvas_background_colour(self) -> str:
         return "#0f0f10" if getattr(self, "theme", "light") == "dark" else "#ffffff"