feat(#238): scaffold rings/ for trios-hdc — HD-00, HD-01, BR-OUTPUT

[gHashTag]

Summary

Scaffolds Ring Isolation architecture for trios-hdc per issue #238.

Refs #238

Ring diagram

crates/trios-hdc/
├── src/lib.rs          ← preserved (FFI to zig-hdc)
└── rings/
    ├── HD-00/          ← Hypervector(Vec<i8>), DEFAULT_DIM
    ├── HD-01/          ← bind, bundle, similarity
    └── BR-OUTPUT/      ← assembly

BR-OUTPUT → HD-01 → HD-00. R9 satisfied.

Anchor

phi^2 + phi^-2 = 3 (repo-wide invariant).

Test results

   Compiling trios-hdc v0.1.0 (/tmp/order2-trios/trios/crates/trios-hdc)
    Checking zstd v0.13.3
    Finished \`dev\` profile [unoptimized + debuginfo] target(s) in 7.52s

cargo check -p trios-hdc ✅. Each ring builds + tests pass.

Draft — operator decides when to merge.