feat: add device manifests and MLS rejoin support

[chgaowei]

Summary

• allow a removed MLS device to replace its inactive local group when an owner-controlled re-add delivers a fresh KeyPackage and Welcome
• add TypeScript Device Manifest parsing, validation, DID document build/update/remove helpers, and public API exports
• add RFC 9421 origin-proof generation and verification with strict sig1 covered-component validation
• add shared-vector and regression coverage for all new behavior

Compatibility and risk

• DID documents without a deviceManifest remain valid and return null from manifest lookup
• existing active MLS bindings do not use the replace-old-group path
• no existing public API is removed
• the main security-sensitive paths validate DID key ownership and relationships, reject private key material, and pin the origin-proof label and covered components

Verification

• cargo fmt --all --check
• cargo test --test group_e2ee_v2_operations: 12 passed
• npm ci
• npm run typecheck
• npm run build: ESM, CJS, and DTS passed
• npm test: 10 files, 92 tests passed
• eslint on the four new TypeScript source/test files: passed

Existing lint debt

The full TypeScript lint command still reports existing formatting and require-await findings in pre-existing tracked files. This PR formats the four newly added files without reformatting unrelated code.