test: split 50-smoke.sx into per-section examples + add errors smoke

Break the monolithic examples/50-smoke.sx into 30 focused per-section examples,
filed into their category blocks (basic/types/comptime/memory/protocols/ffi),
each carrying only the top-level decls its section references (the protocols
section keeps the full preamble — its deps flow through UFCS method calls that
name-based extraction can't see). Outputs verified identical to the original
section blocks.

Add examples/1036-errors-failable-smoke.sx — an end-to-end error-handling example
(the E5.4 work): named + inferred error sets consumed via destructure, try (in
helpers), catch (bare-expr / match-body / diverging / no-binding), or
value-terminator, onfail+defer interleave, and error.X value + {} tag
interpolation.

Remove examples/50-smoke.sx. Suite: 324 passed, 0 failed.

examples/expected/0127-types-using.stdout

@@ -0,0 +1,12 @@
+=== 26. #using ===
+using-x: 1
+using-y: 2
+using-z: 3
+pkt-id: 10
+pkt-ver: 42
+pkt-pay: 99
+sprite-px: 10
+sprite-r: 255
+sprite-scale: 1
+say: hello (len=5)
+n=42