ci(smoke): +200 MB size headroom (base 2950 / omos 3650)

The v2.6.0 pi-devbox CLI-parity additions (pandoc + graphviz + tealdeer,
~200 MB on the base layer) consumed nearly all the ~250 MB headroom that
v1.16.2 restored. v2.6.0 passed 2750/3450 but with a slim margin. Restore
~250 MB headroom so the guardrail catches runaway growth, not routine apt
drift or minor upstream bumps. smoke-test.sh only — no base rebuild; affects
the next tagged release's gate.

scripts/smoke-test.sh

@@ -386,8 +386,15 @@ echo "  Uncompressed size: ${SIZE_MB} MB"
 # ~250 MB headroom avoids a partial-publish + letter-suffix recovery cycle.
 # CI's smoke size print + resolved-versions table records the actual landed
 # sizes; tighten later if they come in low.
-THRESHOLD=2750
-[ "$VARIANT" = "omos" ] && THRESHOLD=3450
+# v2.6.0: bumped +200 MB (2750->2950 base, 3450->3650 omos). The pi-devbox
+# CLI-parity additions (pandoc ~150 MB + graphviz ~40 MB + tealdeer ~5 MB, all
+# on the base layer) consumed almost all of the ~250 MB headroom v1.16.2 had
+# restored — v2.6.0 passed 2750/3450 but with a slim margin. Restoring ~250 MB
+# headroom keeps the guardrail catching *runaway* growth (accidental texlive/
+# chrome bake-in) rather than tripping on routine apt drift or a minor opencode
+# bump. smoke still prints the actual landed size each run; tighten if low.
+THRESHOLD=2950
+[ "$VARIANT" = "omos" ] && THRESHOLD=3650
 if [ "$SIZE_MB" -gt "$THRESHOLD" ]; then
   fail "image size ${SIZE_MB} MB exceeds threshold ${THRESHOLD} MB for variant=$VARIANT"
 else