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/0028-basic-functions.stdout

@@ -0,0 +1,21 @@
+=== 5. Functions ===
+const: 42
+typed-const: 3.140000
+default-init: 0
+implicit-ret: 42
+early-ret: 5
+early-ret2: 99
+void-return: ok
+generic-s32: 42
+generic-f32: 1.500000
+generic-bool: true
+generic-multi: 30
+lambda: 14
+lambda-ret: 5.000000
+local-fn: 7
+fn-nested: 26
+varargs: 15
+spread: 60
+fp: 7
+fp-reassign: 12
+fp-apply: 30