Align architecture doc with current crypto implementation

ARCHITECTURE.md

@@ -12,7 +12,8 @@ Self-hosted Discord alternative with decentralized identity. Each user has a "ho
 - **Client does everything** - syncs, cross-server requests, profile updates
 
 ### Identity System
-- Ed25519 keypair generated on registration
+- Current implementation: secp256k1 keypair/signatures via `crypton` EC
+- Target (planned): Ed25519 migration
 - Private key = proof of identity
 - Public key stored on home server at `/.well-known/users/:username`
 - userId format: `username@serverhost`
@@ -236,8 +237,8 @@ The join flow now:
 
 - **Framework**: Relic 1.0 (Dart web server)
 - **Database**: ObjectBox
-- **Auth**: JWT + Ed25519 signatures
-- **Crypto**: crypton package for Ed25519
+- **Auth**: JWT + secp256k1 signatures (current), Ed25519 (planned)
+- **Crypto**: crypton package (EC)
 - **Password**: bcrypt
 
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