build(fx): example-discovery glob misses examples/Fx/* (161 missing build_info.json warnings per ESP32 build)

[zackees]

Summary

Every Fx-prefixed example (FxNoisePalette, FxFire2012, FxWave, etc.) emits the following on every ESP32 board:

Warning: Exception generating build_info.json: [Errno 2] No such file or directory: '.../build_info_Fx/Fx<Name>.json'
Warning: Failed to parse metadata JSON for build_info.json: Expecting value: line 1 column 1 (char 0)

161 occurrences observed across the ESP audit matrix.

Root cause (suspected)

The example-discovery glob doesn't descend into the examples/Fx/* subdirectory layout, so the per-example build_info.json is never written, then the post-build collector tries to read it and fails.

Why it matters

• Per-Fx-example artifact metadata is silently lost — release tooling / size tracking can't reason about Fx examples.
• Real build_info collector errors will be drowned in this noise.

Proposed fix

Fix the example-discovery glob in the build_info collector to traverse examples/Fx/* (and any other nested example directories). Likely in crates/fbuild-build/src/.../build_info*.rs or crates/fbuild-cli/src/build_info*.rs.

Acceptance: an esp32dev build of any FxNoisePalette example writes its build_info_Fx/FxNoisePalette.json file; CI logs no longer contain the "Exception generating build_info.json" line for Fx examples.

[zackees]

Tracked under fbuild meta-audit: #408