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/removebg.py

@@ -119,22 +119,23 @@ async def rmbg(client: Client, message: Message):
     start = datetime.now()
     await pablo.edit('sending to ReMove.BG')
     input_file_name = cool
-    files = {
-        'image_file': (input_file_name, open(input_file_name, 'rb')),
-    }
-    r = requests.post(
-        'https://api.remove.bg/v1.0/removebg',
-        headers={'X-Api-Key': rmbg_key},
-        files=files,
-        allow_redirects=True,
-        stream=True,
-        timeout=10,
-    )
+    with open(input_file_name, 'rb') as f:
+        files = {
+            'image_file': (input_file_name, f),
+        }
+        r = requests.post(
+            'https://api.remove.bg/v1.0/removebg',
+            headers={'X-Api-Key': rmbg_key},
+            files=files,
+            allow_redirects=True,
+            stream=True,
+            timeout=10,
+        )
     if os.path.exists(cool):
         os.remove(cool)
     output_file_name = r
-    contentType = output_file_name.headers.get('content-type')
-    if 'image' in contentType:
+    content_type = output_file_name.headers.get('content-type')
+    if 'image' in content_type:
         with io.BytesIO(output_file_name.content) as remove_bg_image:
             remove_bg_image.name = 'BG_rem.png'
             await client.send_document(message.chat.id, remove_bg_image, reply_to_message_id=message.id)