TokenPak v1.9.3

Security patch: path-safety hardening for pak install and a default-deny CORS
policy on the proxy's content routes. Additive; one behavior change noted below.

Security

• pak install: added a path-traversal guard (archive entries are resolved and
  confirmed within the target directory), symlinked entries are skipped during
  extraction, and checksum-verified messaging is now honest about what was checked.
• proxy CORS: the /tpk/v1/* JSON routes no longer emit
  Access-Control-Allow-Origin: *. CORS is now default-deny with an
  exact-origin allowlist.

Changed

• proxy CORS (behavior change): a browser app fetching /tpk/v1/* from a
  different origin must now set TOKENPAK_PROXY_CORS_ORIGINS (comma-separated
  exact origins). A matching request Origin is echoed back with Vary: Origin,
  never *. CLI / SDK / MCP clients are unaffected — CORS applies to browsers only.