feat(stdlib): per-decl nominal identity + same-name shadows — close 0105 [stdlib E2]

Make same-name top-level types in different sources DISTINCT nominal types
instead of collapsing last-wins in the type table (issue 0105).

Registration:
- internNamedTypeDecl assigns a per-decl nominal_id and populates
  type_decl_tids. The first author of a name keeps nominal_id 0 (byte-identical
  to pre-E2); a genuine cross-module shadow (>=2 distinct normalized-path
  authors per the import facts) gets a fresh id -> a distinct TypeId.
- mergeFlat/addOwnDecl stop first-wins-dropping per-source decls (named types +
  non-fn const_decls) so every same-name author reaches registration; functions
  and var_decls (incl. #foreign extern globals) keep first-wins.

Resolution (selectNominalLeaf):
- own-author wins; else flatTypeAuthorCount over the transitive flat closure:
  >=2 distinct -> .ambiguous (loud diagnostic + poison); exactly one -> resolved;
  a flat author not yet findByName-registered -> .undeclared stub (not a leak).
- struct-literal type names route through the same source-aware leaf.
- lazyLowerFunction pins the function's own source before resolving its return
  type, so a shadowed signature type resolves in its module, not the caller's.

Codegen:
- mangleTypeName appends __n<id> for nonzero nominal_id so same-name shadows get
  distinct monomorph symbols (struct_to_string__Box vs __Box__n1).

Library hygiene:
- rename trace.sx's compiler-contracted Frame -> TraceFrame (+ the two compiler
  findByName sites) so it never collides with a UI/geometry Frame; the layout is
  structural (getFrameStructType / SxFrame), name-independent.

Examples: 0752-0756 pin the five 0105 cases (distinct fields / same fields /
own-wins / ambiguous / alias per-source); 0170 pins the folded anon-struct-field
regression.

library/modules/trace.sx

@@ -12,7 +12,7 @@
 // still sees the chain) or the (future) failable-`main` wrapper.
 //
 // Frame resolution (ERR E3.0 slice 3a): in compiled code a frame is a pointer
-// to an interned `Frame` the compiler stamped in at the push site, so the
+// to an interned `TraceFrame` the compiler stamped in at the push site, so the
 // location resolves in-process with no DWARF and no symbolizer. (The comptime
 // path — a packed `(func_id, ir_offset)` resolved via the interpreter's IR
 // tables — lands with slice 3b.)
@@ -20,9 +20,13 @@
 
 libc :: #library "c";
 
-// The compiled return-trace frame. Layout MUST match `getFrameStructType` in
-// src/ir/emit_llvm.zig and `SxFrame` in library/vendors/sx_trace_runtime/sx_trace.c.
-Frame :: struct {
+// The compiled return-trace frame. Named `TraceFrame` (not `Frame`) so it never
+// collides with a UI / geometry `Frame` a consumer flat-imports — same-name
+// types are now distinct nominal identities (issue 0105), so a bare `Frame` must
+// resolve unambiguously to the consumer's own. Layout MUST match
+// `getFrameStructType` in src/ir/emit_llvm.zig and `SxFrame` in
+// library/vendors/sx_trace_runtime/sx_trace.c.
+TraceFrame :: struct {
     file: string;
     line: s32;
     col: s32;
@@ -44,7 +48,7 @@ spaces :: (n: s32) -> string {
 // 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` returns the raw stored `u64`; `__trace_resolve_frame` turns it
-// into a `Frame` — by reinterpreting the stamped `*Frame` in compiled code, or
+// into a `TraceFrame` — by reinterpreting the stamped `*TraceFrame` 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;