chore: add totp feature gate (default-on) + data-encoding + qrcode deps

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -298,6 +298,7 @@ dependencies = [
  "argon2",
  "authforge-common",
  "ctap-hid-fido2",
+ "data-encoding",
  "futures-util",
  "hex",
  "nix 0.28.0",
@@ -325,6 +326,7 @@ dependencies = [
  "futures-util",
  "gtk4",
  "libadwaita",
+ "qrcode",
  "tokio",
  "zbus",
 ]
@@ -1823,6 +1825,12 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "qrcode"
+version = "0.14.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d68782463e408eb1e668cf6152704bd856c78c5b6417adaee3203d8f4c1fc9ec"
+
 [[package]]
 name = "quote"
 version = "1.0.45"