ci: add task to build examples on FreeBSD

[lcheylus]

• ci/freebsd_ci.vsh: add task to run v build-examples in FreeBSD CI

• .github/workflows/freebsd_ci.yml: install FreeBSD packages needed to build examples

  • mariadb118-client, postgresql18-client for MySQL/PostgreSQL support
  • alsa-lib, libglvnd, libXi, libXcursor needed by Sokol (audio and graphic support)

✅ Run of "CI FreeBSD" with build-examples (tcc, clang, gcc compiler) task on my personal fork => https://github.com/lcheylus/v/actions/runs/20922528908/job/60111582457

(...)
--------------------------------------------------------------------------------
Summary for building examples: 239 passed, 23 skipped, 262 total. Elapsed time: 81275 ms, on 1 job.
---- Building examples/hot_reload ... ------------------------------------------
v compiler args: "-W -live"
OK    [1/4] C:   438.1 ms, R:     0.000 ms examples/hot_reload/bounce.v
OK    [2/4] C:   441.1 ms, R:     0.000 ms examples/hot_reload/graph.v
OK    [3/4] C:   268.8 ms, R:     0.000 ms examples/hot_reload/message.v
OK    [4/4] C:   447.5 ms, R:     0.000 ms examples/hot_reload/tunnel.v
--------------------------------------------------------------------------------
Summary for building examples/hot_reload: 4 passed, 4 total. Elapsed time: 1598 ms, on 1 job.
2026-01-12T14:23:32.499534Z [INFO ] Finished Build examples in 83291 ms, cmd: `v ci/freebsd_ci.vsh build_examples`

[spytheman]

Thank you @lcheylus 🙇🏻 .
Excellent work.