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/0030-basic-builtins.stdout

@@ -0,0 +1,31 @@
+=== 7. Builtins ===
+out-ok
+sqrt: 3.000000
+sqrt-f64: 4.000000
+sizeof-s32: 4
+sizeof-f64: 8
+sizeof-struct: 8
+alignof-u8: 1
+alignof-s32: 4
+alignof-s64: 8
+alignof-struct: 4
+typeof: int
+typeof-float: float
+typeof-string: string
+typeof-bool: bool
+typeof-struct: struct
+typeof-enum: enum
+typename: Point
+fieldcount: 2
+fieldcount-enum: 3
+fieldname0: x
+fieldname1: y
+fieldname-enum0: red
+fieldname-enum2: blue
+fieldval0: 11
+fieldval1: 22
+fieldidx: 1
+fieldidx-tagged: 0
+fieldidx-tagged2: 2
+cast: 3
+cast-int-f64: 42.000000