fix(e2e): low-battery scenario charge below UPS2's threshold

The Commit 5 bump of low-battery.dev runtime to 900s removed the
critical-runtime fallback that was previously masking a real bug:
UPS2 in tests/e2e/config-e2e-multi-ups.yaml has
low_battery_threshold=15, and the LOW BATTERY trigger uses strict
`<`, so battery.charge=15 never fires UPS2's shutdown. Test 15
(Non-local failure) sat for the full 15-minute job timeout waiting
for a shutdown that wasn't going to come.

Drop battery.charge to 14 so the scenario fires LOW BATTERY against
both UPS1 (threshold 20) and UPS2 (threshold 15), and the
single-UPS tests still exercise the same trigger.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: m4r1k

tests/e2e/scenarios/low-battery.dev

@@ -1,13 +1,17 @@
 # Scenario: Low battery — should trigger shutdown via the LOW BATTERY
-# (charge < 20%) trigger, NOT via the critical-runtime trigger.
-# runtime is set ABOVE the 600 s critical-runtime threshold so the
-# shutdown is unambiguously attributable to the low-battery path; the
-# previous value of 180 s also crossed the critical-runtime threshold,
-# making test failures hard to localise.
+# (charge < threshold) trigger, NOT via the critical-runtime trigger.
+# runtime is ABOVE the 600 s critical-runtime threshold so the shutdown
+# is unambiguously attributable to the low-battery path; the previous
+# value of 180 s also crossed the critical-runtime threshold and made
+# failures hard to localise.
+# charge is 14 (not 15) so it fires both UPS1 (threshold 20, single-UPS
+# tests) AND UPS2 in tests/e2e/config-e2e-multi-ups.yaml (threshold 15).
+# The trigger uses strict `<`, so a value equal to the threshold doesn't
+# fire and Test 15 in multi-ups.sh would never trigger UPS2's shutdown.
 ups.status: OB DISCHRG LB
 ups.load: 35
 
-battery.charge: 15
+battery.charge: 14
 battery.runtime: 900
 battery.voltage: 44.0