chore: drop coglet-alpha selection (#2669)
* chore: drop coglet-alpha selection
Map coglet-alpha and coglet wheel selections to cog-dataclass and remove the pinned coglet-alpha install path.
Update dockerfile generators, wheel parsing, CI runtime matrix, and integration-test conditions to reflect the removal.
* warn on fast builds and fall back to standard
* test: write outbox atomically in double-fork
* test: remove monobase integration cases
