feat(gates): add gate6 probe generation

[gowdaharshith1998-lang]

Summary

• Adds Gate 6 probe generation with curated boundary probes, deterministic Hypothesis-backed random probes, and Gate 5 counterexample injection.
• Adds probe-set details for receipt wiring, including partial custom-type probe metadata and the 200-probe cap.
• Extends the probe runner to consume default-construction and special floating-point markers so custom objects, NaN, and infinities survive the JSON subprocess boundary.

EARS Coverage

• R-5.1: generate_probes returns boundary probes plus requested random probes.
• R-5.2: Gate 5 failed diverging_input is injected into the Gate 6 probe set.
• R-5.3: unknown parameter types include null/default-construction probes and mark details.partial.

Verification

• bash src/omnix/semantic/java/jvm/build.sh
• pytest tests/gates/test_gate6_probes.py -q
• pytest tests/gates/test_gate6_probes.py tests/gates/test_gate6_harness.py tests/semantic/java/test_vendor_integrity.py -q
• python -m ruff check src/omnix/gates/gate6_equivalence tests/gates/test_gate6_probes.py tests/gates/test_gate6_harness.py
• python -m mypy src/omnix/gates/gate6_equivalence
• pytest tests/gates/ tests/semantic/java/test_vendor_integrity.py -q
• pytest tests/ -q --tb=line
• npx gitnexus detect-changes --scope staged: HIGH risk due expected probe-runner main-flow changes; full pytest passed afterward.

Notes

• Stacked on Phase 4 PR because earlier M2 PRs are still awaiting merge.
• GitHub Actions may not start due the known account billing/spending-limit block documented in the dispatch.