[Thermo-Nuclear][Wave 2] Comprehensive -uall untracked file hygiene across host drivers and scripts #647

Parent #645 (Program Epic). Detail reports: docs/audit/thermo-nuclear-636/02_worktree_audit_and_untracked_hygiene.md and 03_contract_tests_and_domain_modeling.md.

Problem

1. While worktree-audit.sh was hardened with -uall in PR test(cross-port): host-scoped contract tests for 0.9.95 negative invariants (#638) #644, scripts/drivers/omp.py line 143 (_isolation_residue) calls git status --porcelain without -uall. When status.showUntrackedFiles = no is configured, untracked child residue left in the parent checkout is omitted from status output, causing tree_clean to falsely evaluate to True (false PASS on runtime workspace isolation).
2. scripts/sync-antigravity-plugin.py line 287 calls git status --porcelain without -uall, risking publishing untracked files without warning.
3. In tests/test_cross_port_contracts.py, safe_terminate_process tests token mismatch, but does not guard against non-positive PIDs (pid <= 1), which in POSIX signals can terminate process groups or the entire session.

Scope

• Update _isolation_residue in scripts/drivers/omp.py to pass "-uall".
• Update scripts/sync-antigravity-plugin.py line 287 to pass "-uall".
• In tests/test_cross_port_contracts.py, add pid <= 1 guards to safe process termination contracts.
• Add regression tests proving tree_clean is False when untracked child files exist under status.showUntrackedFiles = no.