ERR/E3.0 (slice 3b): comptime trace resolution

#run failures now print the same `func at file:line:col` trace as
runtime, resolved in-process via the interpreter's IR/source tables.

- Read-side context-split op `.trace_resolve` (mirror of .trace_frame),
  lowered from a name-recognized `__trace_resolve_frame(u64) -> Frame`.
- emit_llvm: inttoptr the operand to *Frame + load (the value
  .trace_frame stamped in).
- interp: unpack (func_id << 32 | span.start); resolve func/file from
  module.functions and line/col via SourceLoc.compute over a new
  source_map (setSourceMap wired at every production interp site).
- trace.sx: frame_at -> u64; to_string routes each frame through
  __trace_resolve_frame, so one source works in both machines.

Compiled path behavior unchanged (243/244/247 identical; it now loads
via the op). New examples/253-comptime-trace.sx exercises the comptime
path. Gates: zig build, zig build test, run_examples.sh -> 291 passed.

examples/253-comptime-trace.sx

@@ -0,0 +1,33 @@
+// Comptime return-trace resolution (ERR E3.0 slice 3b). A `#run` block that
+// raises, propagates via `try`, and catches the error, then formats the trace
+// with `trace.print_current()`. At comptime a frame is a packed
+// `(func_id, span.start)` (not a `*Frame`); the interpreter's `.trace_resolve`
+// unpacks it and resolves `file:line:col` via the module + source map — so the
+// comptime trace prints the same `func at file:line:col` form as a runtime one.
+// Expected exit: 0 (the error is caught; the trace is printed during the build).
+
+#import "modules/std.sx";
+trace :: #import "modules/trace.sx";
+
+TErr :: error { Bad };
+
+leaf :: () -> !TErr {
+    raise error.Bad;
+}
+
+mid :: () -> !TErr {
+    try leaf();
+}
+
+probe :: () {
+    mid() catch e {
+        print("comptime caught {}\n", e);
+        trace.print_current();
+    };
+}
+
+#run probe();
+
+main :: () -> s32 {
+    return 0;
+}