ci(*): add build/test app scripts, workflow

[vdice]

Alternative to #65

• Adds GH workflow to run parallelized app builds (reduces time from ~15 mins (in ci(*): test samples and tutorials #65) to just over 2 mins)
• Adds a preliminary test script -- but too large a number of apps require specific testing, so holding off on adding to CI until we come up with a plan there (if we ever want to)
• Adds a few setup Make targets for apps that require a bit of prep before building or running

Sample run: https://github.com/vdice/fwf-examples/actions/runs/16647598287

(Not sure why the checks aren't showing -- maybe the workflow needs to merge first. Here's a sample PR on my fork with the checks: vdice#3)