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/0025-basic-literals.stdout

@@ -0,0 +1,18 @@
+=== 1. Literals ===
+decimal: 42
+hex: 255
+binary: 10
+float: 3.140000
+f64: 2.718281
+true: true
+false: false
+escapes: hello	world
+multiline: line1
+line2
+heredoc: raw heredoc
+
+undef-then-set: 77
+enum-lit: .green
+null-ptr: null
+string-len: 5
+empty-string: 0