Finding current when short-circuiting the terminals
Applying a source conversion to the voltage source V1 will make the job easy.
A voltage source V in series with a resistance R can be replaced (Across its two terminals) with a Current source of value V/R with a resistance R in parallel with it.
The proof for this result may be found online in sources such as this.
After performing such a conversion the short circuit current will be the sum of the two sources and independent of R2.