F-040: design Bazel adapter mapping

[stepango]

Summary

• Design-only ticket F-040: new docs/BAZEL-ADAPTER.md (408 lines) mapping forma-core types + restriction graph to Bazel packages/labels/rules/visibility.
• JVM-first kit (jvm.api…jvm.binary); hybrid visibility + check backstop; FormaProjectModel + generate/check SPI; F-041/F-042 plan.
• Cross-links: VISION, forma-core-api, ARCHITECTURE, README, JVM-TARGETS, JVM-SAMPLE.
• TICKETS: F-040 done; F-041/F-042 remain todo.

Test plan

• Pure docs — no product code changes
• Doc covers 10 design sections; <1000 lines
• Cross-links resolve
• Reviewer skim of visibility strategy + spike order for F-041