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/0608-comptime-comptime.sx

@@ -0,0 +1,83 @@
+#import "modules/std.sx";
+#import "modules/math/math.sx";
+#import "modules/compiler.sx";
+#import "modules/test.sx";
+pkg :: #import "modules/testpkg";
+
+add :: (a: s32, b: s32) -> s32 { a + b; }
+
+mul :: (a: s32, b: s32) -> s32 { a * b; }
+
+// #run compile-time constants
+CT_VAL :: #run add(10, 15);
+
+CT_MUL :: #run mul(6, 7);
+
+CT_CHAIN :: #run add(CT_VAL, 5);
+
+// #run compile-time optional tests
+
+// #run compile-time optional tests
+ct_opt_coalesce :: () -> s32 {
+    x: ?s32 = 42;
+    y: ?s32 = null;
+    return (x ?? 0) + (y ?? 99);
+}
+
+ct_opt_unwrap :: () -> s32 {
+    x: ?s32 = 77;
+    return x!;
+}
+
+ct_opt_guard :: () -> s32 {
+    x: ?s32 = 10;
+    if x == null { return -1; }
+    return x;
+}
+
+CT_OPT_COALESCE :: #run ct_opt_coalesce();
+
+CT_OPT_UNWRAP :: #run ct_opt_unwrap();
+
+CT_OPT_GUARD :: #run ct_opt_guard();
+
+// #insert helpers
+
+// #insert helpers
+gen_code :: () -> string {
+    return "print(\"insert-ok\\n\");";
+}
+
+gen_val :: () -> string {
+    return "print(\"insert-gen: {}\\n\", 42);";
+}
+
+// --- Error handling (failable functions: sets, raise/try/catch/or/onfail) ---
+
+main :: () {
+
+    // ========================================================
+    // 8. COMPILE-TIME
+    // ========================================================
+    print("=== 8. Comptime ===\n");
+
+    // #run constant
+    print("run-const: {}\n", CT_VAL);
+
+    // #run with expression
+    print("run-expr: {}\n", CT_MUL);
+
+    // #run chained dependency
+    print("run-chain: {}\n", CT_CHAIN);
+
+    // #run comptime optionals
+    print("ct-opt-coalesce: {}\n", CT_OPT_COALESCE);           // ct-opt-coalesce: 141
+    print("ct-opt-unwrap: {}\n", CT_OPT_UNWRAP);               // ct-opt-unwrap: 77
+    print("ct-opt-guard: {}\n", CT_OPT_GUARD);                 // ct-opt-guard: 10
+
+    // #insert with function
+    #insert gen_code();
+
+    // #insert additional
+    #insert gen_val();
+}