[samgbafa]

Changes

• Read v1 and TCW2 key-wrap envelopes for network and named keys.
• Add HKDF-SHA256 v2 wrapping with canonical authenticated context.
• Keep v1 response writes by default; opt in with [global.encryption_network] key_wrap_v2 = true or TINYCLOUD_ENCRYPTION_NETWORK__KEY_WRAP_V2=true.
• Keep network/key descriptor and payload schemas unchanged.
• Add shared SDK interoperability fixtures and version-matrix coverage.

Verification

• cargo test -p tinycloud-core encryption_network: 229 passed; 10 existing PostgreSQL-gated paths did not connect locally.
• Final backend regression run: 22 passed.
• cargo test -p tinycloud-node encryption_network_: 3 passed.
• cargo build -p tinycloud-node --bin tinycloud: passed.
• cargo clippy -p tinycloud-core -p tinycloud-node --all-targets -- -D warnings: passed.
• cargo fmt --all -- --check: passed.
• Actual local SDK→Rust→SDK HTTP roundtrips passed all four request/response wrap-version combinations, including signature verification.

Companion SDK PR: TinyCloudLabs/js-sdk#906 (593f05173d52dd3f1b9424c7638ca7591cb9d589).
Phase 1 only: writers remain v1 by default. No data migration or deployment included.

Details: TC-2518