campaign(qwen38): the calibration floor is 12M tokens

Frank's rule: the served iq4r this arm competes with was calibrated on a
10M-token set, so the arm is calibrated at least as deeply. The floor was
lowered to 1.5M on the vendor's '10M beats 1M by under 1%' note; that
measures the vendor's own plate, not ours — the arm is judged against a
10M-calibrated reference, so cutting the calibration 6x to save wall clock
buys a worse position on the only comparison that matters.

One round of the re-chunked corpus is ~9.31M tokens, so a 12M floor seals
in round 1 plus part of round 2. A round that seals nothing is normal (the
floor is pooled) and round_verdict treats it as continue, never failure.

Also fixes tests/qwen38_campaign.bats' window dry run: its fixture lands on
/tmp (a 16 GiB tmpfs) where the 60 GiB seal preflight can never pass, so the
test now uses the documented Q38_CALIB_MIN_FREE_MIB override instead of
asserting environment luck.

tests/qwen38_reference.bats

@@ -157,11 +157,11 @@ flag_value() {
     [[ "$output" != *"--vram-kv-mib"* ]]
 }
 
-@test "the calib dry run opens the tap at the 1.5M floor, on the latest pin, and serves on 7770" {
+@test "the calib dry run opens the tap at the 12M floor, on the latest pin, and serves on 7770" {
     run bash "$RUNNER" calib --dry-run
     [ "$status" -eq 0 ]
     flat="$(oneline)"
-    [[ "$flat" == *"-e RADIANCE_CALIB_TOKENS=1500000"* ]]
+    [[ "$flat" == *"-e RADIANCE_CALIB_TOKENS=12000000"* ]]
     [[ "$flat" == *"-e RADIANCE_CALIB_DIR=/data/calib"* ]]
     # the tap producer is the campaign's own pin (latest radiance), not production's
     [[ "$flat" == *"radiance@sha256:69add58f"* ]]