ci: use canonical dogfood URL #256

Job	Run time
Preflight (fmt, clippy, check, agents-md)	38s
Docs (build, no deploy)	34s
cargo-deny	39s
Size guard (<25 MiB)	2m 1s
Test (macos-latest)	1m 6s
Test (ubuntu-latest)	1m 13s
Determinism	38s
MSRV (1.95)	19s
Test (windows-latest)	2m 44s
Coverage	1m 24s
	11m 16s

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