fix: prevent Linux keyring auth corruption

[savass33]

Summary

• compress the shared Linux Secret Service payload to avoid KWallet 8 KiB truncation
• keep compatibility with legacy plain JSON records
• reject oversized writes instead of silently storing corrupted data
• allow a successful OAuth login to replace a malformed native record
• release as @verboo/code 0.15.27

Validation

• quality gate: 339/339 isolated test files passed
• terminal/PTY gate: 33/33 tests passed
• package tarball checksum verified
• local Verboo and /codex authentication tested end-to-end

The full CI release workflow remains the final cross-platform validation before npm publication.