XY-1281: Establish Program and Objective authority semantics

[acgxv]

Summary

• introduce authoritative Program and finite Objective domain semantics
• remove Goal from the vNext product/database authority path
• enforce request-scoped receipts, concurrent identity convergence, revision-bound completion evidence, and PostgreSQL/Rust timestamp alignment
• define successful ManagedRun completion through explicit WorkItem acceptance and validation

Verification

• cargo test -p decodex-core -p decodex-postgres --all-targets --all-features
• python3 tests/scripts/test_vnext_architecture.py
• SCCACHE_DISABLE=1 python3 scripts/vnext/postgres_store_test.py

Breaking vNext authority change. Linear: XY-1281