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.

library/modules/trace.sx

@@ -31,10 +31,12 @@ Frame :: struct {
 
 // The error-trace buffer C API (library/vendors/sx_trace_runtime/sx_trace.c),
 // linked in for the JIT and auto-injected for AOT when traces are used.
-// `frame_at` hands back the stamped `*Frame` (the compiler stored its address).
+// `frame_at` returns the raw stored `u64`; `__trace_resolve_frame` turns it
+// into a `Frame` — by reinterpreting the stamped `*Frame` in compiled code, or
+// by resolving the packed `(func_id, span.start)` in the comptime interpreter.
 sx_trace_len       :: () -> u32 #foreign;
 sx_trace_truncated :: () -> u32 #foreign;
-sx_trace_frame_at  :: (i: u32) -> *Frame #foreign;
+sx_trace_frame_at  :: (i: u32) -> u64 #foreign;
 
 write :: (fd: s32, buf: [*]u8, count: usize) -> isize #foreign libc;
 
@@ -51,7 +53,7 @@ to_string :: () -> string {
 
     i : u32 = 0;
     while i < n {
-        f := sx_trace_frame_at(i);
+        f := __trace_resolve_frame(sx_trace_frame_at(i));
         line := format("  {} at {}:{}:{}\n", f.func, f.file, f.line, f.col);
         result = concat(result, line);
         i = i + 1;