feat(wasm): add generate_device_keypair + get_field_history bindings

generate_device_keypair returns an ed25519 keypair as JSON with hex pubkey
and base64 private key. get_field_history extracts tracked field history
from a decrypted item for the popup's history view.

Co-Authored-By: Claude <noreply@anthropic.com>

crates/relicario-wasm/Cargo.toml

@@ -15,6 +15,10 @@ serde_json = "1"
 serde = { version = "1", features = ["derive"] }
 zeroize = "1"
 getrandom = { version = "0.2", features = ["js"] }
+ed25519-dalek = { version = "2", features = ["rand_core"] }
+base64 = "0.22"
+hex = "0.4"
+rand = "0.8"
 
 [dev-dependencies]
 wasm-bindgen-test = "0.3"