Implement the Jolt physics backend

[snkmcb]

Summary

• add a Jolt Physics backend and integrate it with the backend/runtime build
• support installation and downstream consumption with pinned Jolt 5.5.0 version and ABI checks
• add backend, installed-consumer, Windows/Linux, and OpenStrata coverage
• document the dependency and enable the Jolt path in source CI

Review follow-up

Addressed all findings from the local Codex review:

• reject incompatible installed Jolt targets and versions
• reject dynamic masses that cannot be represented safely by Jolt
• select the nearest eligible ground support before using normal as a tie-break
• configure hosted Linux Jolt builds as Release
• exclude the reserved invalid Jolt object layer

Validation

• Windows Jolt suite: 11/11 passed
• Windows no-Jolt suite: 10/10 passed
• Linux Jolt build and focused backend tests passed
• installed-consumer positive and incompatible-ABI negative tests passed
• ost build --intent jolt passed
• ost test --intent jolt passed: 11/11
• ost ci validate --json passed
• git diff --check passed