Perf: bump parallel workers 4 -> 6 (injection freed the CPU)

Pre-injection, 6 workers had occasional UI timeouts (the UI login was
CPU-heavy). With the login skipped via token injection, the machine has
headroom: a 6-worker run of the four heaviest suites passed 59/0/1 (was 1
failure pre-injection). 8 still thrashes. ~33% more parallelism, no coverage
cost.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

iosApp/run_ui_tests.sh

@@ -34,10 +34,10 @@ SCHEME="HoneyDueUITests"
 API_SCHEME="HoneyDueAPITests"
 TARGET="HoneyDueUITests"
 DESTINATION="platform=iOS Simulator,name=iPhone 17 Pro"
-# Data isolation removed cross-suite races, but each test now relaunches the
-# app + creates an account, so the bottleneck is CPU/simulator. 4 is the reliable
-# sweet spot on a Mac mini (8 thrashed the simulators -> UI timeouts). Override via arg 2.
-WORKERS=4
+# Workers. Bottleneck is CPU/simulator (each test relaunches the app). Token
+# injection removed the CPU-heavy UI login, so 6 is now reliable (validated: 0
+# failures on the heaviest suites; 8 still thrashes). Override via arg 2.
+WORKERS=6
 
 # Suites that run in their own phases — excluded from the parallel phase.
 PHASE_MANAGED=(