v0.5.0.dev12: Prepare Potbot 0.5.0.dev12 source preview (#45)

Source preview 0.5.0.dev12 includes the verified default-branch changes after dev11.

The exact release candidate passed the full source, roadmap, native, PostgreSQL, browser and sandbox CI checks. The package and runtime version identities agree. Published package evidence and native acceptance remain scoped to the tested hosts and integrations.