feat(storage): persist kanren CrossLangInteraction as hexads (issue #33 follow-up) (#61)

## Summary
- Adds a `HexadSemantic.crosslang: Option<CrosslangSemantic>` facet and
a
  `build_crosslang_hexads(...)` helper that drives the kanren
`CrossLangAnalyzer` per repo (ingest → extract → load_rules → analyze →
  query_interactions) and emits one hexad per derived
  `CrossLangInteraction`.
- New env var `PANIC_ATTACK_STORE_CROSSLANG_HEXADS` (separate from
  `PANIC_ATTACK_STORE_FINDING_HEXADS`) opts a run into emission;
  `persist_assemblyline_report` writes to `<dir>/hexads/crosslang/`
  file-side only.
- Adds `load_crosslang_hexads(base_dir)` so the paired query-evaluator
PR
  can match against persisted facts; falls back to empty `Vec` when the
dir is missing (the evaluator treats that as "use co-occurrence proxy").

## Why
Tightens the `(crosslang :from :to)` query from a same-repo
co-occurrence
proxy to a true FFI/cross-language reachability check against
persisted kanren-derived facts. PR 1 of a 2-PR stack; PR 2 switches the
evaluator over while preserving fall-back semantics.

## Test plan
- [x] `cargo test --lib` — 252 tests pass, including 4 new
      `storage::tests::*crosslang*` cases (build-empty, build-from-FFI,
      write/read roundtrip + missing-dir, env-var default-off + opt-in).
- [x] `cargo clippy --all-targets -- -D warnings` clean.
- [x] `cargo fmt --all` no diff.

Stacks under: issue #33 S1/S2/S3 PRs (#55, #56, #57, #58). Filed against
`main` per orphan-trap rule.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath