ci(*): test samples and tutorials

[vdice]

• Adds automation to build and test sample and tutorial apps (note TODO re: testing some apps that require additional logic to test)

I wrote much of this automation locally to test a recent PR (#61) which updated many sample apps; hopefully it proves useful.

Note: in the current form, this automation does add substantial time to each PR -- approx. 15-16ish minutes. That's a decent amount. We could either:

1. Only build/test on merges to main (commit author of merge commit for failed workflow run would/should get pinged)
2. Accept the added wait time short-term, creating a follow-up to parallelize (make -jN? GH workflow update?)
3. Block this addition on parallelization or otherwise cutting down time to run tests

Draft for now pending feedback on ^^

Sample run: https://github.com/vdice/fwf-examples/actions/runs/16421708939/job/46401717284

[vdice]

Closing in favor of #68