v1.9.1: PNG Material Design icons — 28 icons, dark/light theme, HiDPI, graceful Unicode fallback

- 56 PNG icons (28 unique × 2 color variants) from Material Design Icons (round style, 96×96px)
- core/icons.py: ctk_icon(), make_icon_button(), reconfigure_icon_button() with CTkImage cache
- Updated 15 GUI files: app.py, sidebar.py, server_dialog.py, all tabs
- build.py: auto-include assets/icons/ in PyInstaller bundle, patch rollover at 99→minor+1
- tools/download_icons.py: icon download script
- Automatic dark↔light theme switching via CTkImage dual-image support

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

gui/tabs/s3_tab.py

@@ -12,7 +12,7 @@ from tkinter import ttk, filedialog
 import customtkinter as ctk
 from core.s3_client import S3Client
 from core.i18n import t
-from core.icons import icon_text
+from core.icons import icon_text, make_icon_button
 from gui.tabs.query_tab import apply_dark_scrollbar_style
 
 
@@ -103,32 +103,32 @@ class S3Tab(ctk.CTkFrame):
         btn_frame = ctk.CTkFrame(header, fg_color="transparent")
         btn_frame.pack(side="right")
 
-        self._back_btn = ctk.CTkButton(
-            btn_frame, text=icon_text("back", t("s3_back")), width=80,
+        self._back_btn = make_icon_button(
+            btn_frame, "back", t("s3_back"), width=80,
             command=self._go_back, state="disabled",
         )
         self._back_btn.pack(side="left", padx=(0, 5))
 
-        self._refresh_btn = ctk.CTkButton(
-            btn_frame, text=icon_text("refresh", t("s3_refresh")), width=100,
+        self._refresh_btn = make_icon_button(
+            btn_frame, "refresh", t("s3_refresh"), width=100,
             command=self._refresh,
         )
         self._refresh_btn.pack(side="left", padx=(0, 5))
 
-        self._upload_btn = ctk.CTkButton(
-            btn_frame, text=icon_text("upload", t("s3_upload")), width=100,
+        self._upload_btn = make_icon_button(
+            btn_frame, "upload", t("s3_upload"), width=100,
             command=self._upload,
         )
         self._upload_btn.pack(side="left", padx=(0, 5))
 
-        self._download_btn = ctk.CTkButton(
-            btn_frame, text=icon_text("download", t("s3_download")), width=110,
+        self._download_btn = make_icon_button(
+            btn_frame, "download", t("s3_download"), width=110,
             command=self._download,
         )
         self._download_btn.pack(side="left", padx=(0, 5))
 
-        self._delete_btn = ctk.CTkButton(
-            btn_frame, text=icon_text("delete", t("s3_delete")), width=100,
+        self._delete_btn = make_icon_button(
+            btn_frame, "delete", t("s3_delete"), width=100,
             fg_color="#dc2626", hover_color="#b91c1c",
             command=self._delete,
         )