Refactor: Split the __main__.py monolith into focused modules

[D-VR]

Extract the first low-risk parts out, and move everything into fitting submodules.
This PR mostly moves code around without modifying the actual functions.
First step in addressing #97, next step is breaking down the syncMyMoodle class in app.py as it's still way too big

New modules:

• constants, totp, node: leaf values/helpers
• context: SyncContext state holder (owns per-run state, wired transitionally via delegating properties on SyncMyMoodle)
• pathing, filters: sanitize/path-safety and skip/prefix logic, now pure functions taking config explicitly
• storage: gzip-JSON + cookie serialization
• cli : main() + argparse, console script repointed to syncmymoodle.cli:main, __main__.py is now just a thin shim
• app: now holds the main syncMyMoodle class