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

images/unsplash2.py

@@ -40,7 +40,7 @@ async def download_image(url):
 
 
 @Client.on_message(filters.command(['unsplash2', 'usp2'], prefix) & filters.me)
-async def imgsearch(client: Client, message: Message):
+async def imgsearch(_client: Client, message: Message):
     if len(message.command) < 2:
         await message.edit('Usage: `img [number] <query>`', parse_mode=enums.ParseMode.MARKDOWN)
         return