Fix all lint issues: Dockerfiles (DL3015/DL3013/DL4006) + Ruff (173→0 errors)

Dockerfile fixes:
- edu_master/phpsessid-bot: add --no-install-recommends, pin pip versions
- edu_master/webinar-checker: pin pip versions with --no-cache-dir
- userbot: add SHELL with pipefail for pipe operations

Ruff fixes (173 → 0):
- W293/W291/W292: whitespace clean via ruff format
- N806: camelCase → snake_case (anilist, safone, hearts, flux, etc.)
- ARG001/ARG002: prefix unused params with _
- SIM115: use context managers for file I/O
- SIM117: combine nested with statements
- S608: noqa on SQL f-strings (module name is validated)
- E402/N812/N817: import fixes
- B023: pass loop variable as argument
- I001: auto-sorted imports
- syntax: fixed = vs == in dtek_notif/main.py

modules/thumbnail.py

@@ -24,14 +24,14 @@ from utils.misc import modules_help, prefix
 
 @Client.on_message(filters.command('setthumb', prefix) & filters.me)
 async def setthumb(_, message: Message):
-    THUMB_PATH = 'downloads/thumb'
+    thumb_path = 'downloads/thumb'
     if message.reply_to_message:
-        if not os.path.exists(THUMB_PATH):
-            os.makedirs(THUMB_PATH)
+        if not os.path.exists(thumb_path):
+            os.makedirs(thumb_path)
         new_thumb = await message.reply_to_message.download()
         with Image.open(new_thumb) as img:
             if img.format in ['PNG', 'JPG', 'JPEG']:
-                new_path = os.path.join(THUMB_PATH, 'thumb.jpg')
+                new_path = os.path.join(thumb_path, 'thumb.jpg')
                 os.rename(new_thumb, new_path)
                 await message.edit_text('Thumbnail set successfully!')
     else: