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>

Cargo.lock

@@ -162,6 +162,12 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c08606f8c3cbf4ce6ec8e28fb0014a2c086708fe954eaa885384a6165172e7e8"
 
+[[package]]
+name = "base64"
+version = "0.22.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
+
 [[package]]
 name = "base64ct"
 version = "1.8.3"
@@ -1557,8 +1563,12 @@ dependencies = [
 name = "relicario-wasm"
 version = "0.1.0"
 dependencies = [
+ "base64",
+ "ed25519-dalek",
  "getrandom 0.2.17",
+ "hex",
  "image",
+ "rand",
  "relicario-core",
  "serde",
  "serde-wasm-bindgen",