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

userbot/modules/direct.py

@@ -30,11 +30,11 @@ def subprocess_run(cmd):
         executable='bash',
     )
     talk = subproc.communicate()
-    exitCode = subproc.returncode
-    if exitCode != 0:
+    exit_code = subproc.returncode
+    if exit_code != 0:
         reply += (
             '```An error was detected while running the subprocess:\n'
-            f'exit code: {exitCode}\n'
+            f'exit code: {exit_code}\n'
             f'stdout: {talk[0]}\n'
             f'stderr: {talk[1]}```'
         )