Consolidate the Install identity schema contract

[BrettKinny]

Closes #106

What changed

• defines the authoritative FORMAT=1 field order and semantic rules in a machine-readable schema
• adds an ADR preserving standalone Bash and PowerShell bootstrap behavior
• verifies all four readers and both writers against the schema in CI
• drives 18 shared valid and adversarial fixtures through both Bash adapters and the native PowerShell test
• rejects repeated path separators consistently across adapters

Why

The lifecycle adapters duplicated their Install identity contract. Existing CI checked PowerShell field lists but could not detect shared semantic drift; Bash accepted a non-normalized path form that PowerShell rejected.

Validation

• complete executable repository shell suite
• lifecycle install-state, ownership, release-identity, and static suites
• Python compile and JSON parsing
• git diff --check

Native PowerShell execution is intentionally left to the existing Windows CI job because pwsh is not installed on the development workstation.