refactor: split if/else in Accounts.User password helpers

- do_hash_password/3: move the changeset.valid? branch out of the
  `if` into apply_hash/3, dispatched on the boolean. The bcrypt 72-byte
  cap and plaintext-scrubbing steps now live in one clear function head.
- validate_current_password/2: dispatch on valid_password?/2 via
  check_current_password/2 so the add_error branch is its own clause.

No behavior change; all 24 Accounts tests still pass and dialyzer stays
clean.

lib/aprsme/accounts/user.ex

@@ -84,19 +84,22 @@ defmodule Aprsme.Accounts.User do
   end
 
   defp do_hash_password(changeset, true, password) when is_binary(password) do
-    if changeset.valid? do
-      changeset
-      # If using Bcrypt, then further validate it is at most 72 bytes long
-      |> validate_length(:password, max: 72, count: :bytes)
-      |> put_change(:hashed_password, Bcrypt.hash_pwd_salt(password))
-      |> delete_change(:password)
-    else
-      changeset
-    end
+    apply_hash(changeset.valid?, changeset, password)
   end
 
   defp do_hash_password(changeset, _, _), do: changeset
 
+  # Bcrypt has a 72-byte key cap, so we enforce that before hashing and
+  # drop the plaintext from the changeset so it can't accidentally leak.
+  defp apply_hash(true, changeset, password) do
+    changeset
+    |> validate_length(:password, max: 72, count: :bytes)
+    |> put_change(:hashed_password, Bcrypt.hash_pwd_salt(password))
+    |> delete_change(:password)
+  end
+
+  defp apply_hash(false, changeset, _password), do: changeset
+
   defp maybe_validate_unique_email(changeset, opts) do
     validate_email? = Keyword.get(opts, :validate_email, true)
     do_validate_unique_email(changeset, validate_email?)
@@ -200,10 +203,9 @@ defmodule Aprsme.Accounts.User do
   Validates the current password otherwise adds an error to the changeset.
   """
   def validate_current_password(changeset, password) do
-    if valid_password?(changeset.data, password) do
-      changeset
-    else
-      add_error(changeset, :current_password, "is not valid")
-    end
+    check_current_password(valid_password?(changeset.data, password), changeset)
   end
+
+  defp check_current_password(true, changeset), do: changeset
+  defp check_current_password(false, changeset), do: add_error(changeset, :current_password, "is not valid")
 end