chore: ignore the generated UI source and drop the stale variant help text

scripts/embed-frontend.sh generates src/ui/embedded_assets.c into the SOURCE
tree (the linker needs it beside the other UI sources, and scripts/clean.sh
removes it). It was never gitignored, so a --with-ui build leaves a large
untracked generated file sitting in `git status` waiting to be committed by
accident. It predates this branch, but this change makes that build path the
default one, so close it here.

smoke-local.sh still documented a `ui` argument that no longer exists.

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>

.gitignore

@@ -48,6 +48,9 @@ private/
 build/
 node_modules/
 graph-ui/dist/
+# Generated by scripts/embed-frontend.sh into the source tree (the linker needs
+# it beside the other UI sources). Removed by scripts/clean.sh; never committed.
+src/ui/embedded_assets.c
 
 # Generated reports
 BENCHMARK_REPORT.md

scripts/smoke-local.sh

@@ -21,9 +21,10 @@ destination override neutralized.
 
 Arguments:
   <binary>     Product binary to smoke (e.g. build/c/codebase-memory-mcp).
-  ui           Mirror the -ui asset naming AND require the embedded UI:
-               Phase 15's "no assets" outcome becomes a FAILURE
-               (SMOKE_REQUIRE_UI=1), so a standard binary cannot pass a ui run.
+
+One composition ships and it carries the embedded UI, so Phase 15's "no assets"
+outcome is always a FAILURE here (SMOKE_REQUIRE_UI=1): a binary built without
+--with-ui cannot pass this smoke.
 
 Environment:
   CBM_SMOKE_ARTIFACT_DIR   Release mode: an EXTRACTED release artifact