Very nice idea. I'm really glad that someone is brave enough to do something like this. The only risk I see with this, is that you might cause price increase for ads, if you will have substantial amount of users, which will make your service more expensive.
Good Luck!
Well, some of web apps are already blackboxes, due to use of languages which are compiled to javascript (JS output usually is completely unreadable) and tools like Google Closure Compiler. WebAssembly won't make much of a difference.
If you hate your job, you better leave it. No matter how professional you are, it will show up on your quality of work, you will start slacking off eventually, and it will make you worse programmer than you are now.
The fault is entirely on the company who hired you. They've seen your CV, they knew what kind of work you were going to do. I doubt they've even asked about this stuff.
So it isn't your fault, and staying at this job will only hurt you. So you should find another job (but be more careful in choosing your next company).
Not everyone is using GitHub for source hosting, there quite a few companies, which use internally some other VCS (like Perforce) and publish the sources on GitHub.