nVelope Client v0.1.0 Beta Release 4

Fixes:

PoW mining was ~12x slower than intended:

The PoW benchmark measured a tiny synthetic event, so its hash rate overstated real-world mining speed ~12x. A "22-minute" (29-bit) recipient policy actually took ~4.5 hours of mining.

Mining now runs in parallel worker threads with native SHA-256: ~28x faster overall and no UI freeze while mining. A 29-bit target completes in ~10 minutes on an 8-core machine.

The benchmark now measures a realistic envelope-sized payload, so published recipient policies match their intended mining time.

Action needed after upgrading: re-run the PoW benchmark in Settings, and re-publish your recipient policy — policies published with older builds are ~3.6 bits (≈12x) harder than intended.

Also updated defaults for PoW so they aren't starting so high to encourage people to message each other.

Other updates:

• Reply All, full recipient lists in headers, From/To headers on threaded messages
• Wizard cancel at any point
• Existing-certificate detection when importing an nsec
• Identity import from a .vault backup.