chore: extract common skill conventions into CLAUDE.md #2907

Job	Run time
Java_21 (webkit)	8m 48s
stable (windows-latest, msedge)	30m 19s
Java_21 (chromium)	5m 47s
dev (ubuntu-latest, webkit)	9m 31s
stable (macos-latest, msedge)	12m 33s
Java_21 (firefox)	11m 20s
dev (ubuntu-latest, firefox)	12m 57s
dev (windows-latest, chromium)	10m 58s
dev (macos-latest, firefox)	16m 55s
dev (windows-latest, firefox)	21m 13s
stable (macos-latest, chrome)	10m 26s
dev (macos-15-xlarge, webkit)	7m 45s
dev (macos-latest, chromium)	6m 51s
stable (windows-latest, chrome)	13m 45s
dev (windows-latest, webkit)	30m 16s
stable (ubuntu-latest, chrome)	7m 12s
dev (ubuntu-latest, chromium)	6m 8s
	3h 42m 44s

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