fix: trim access token on save to prevent illegal header chars

Trailing newlines (0x0a) in pasted tokens caused OkHttp to throw
IllegalArgumentException when setting the access-token header.
Trimming on save prevents whitespace from reaching the network layer.

app/src/main/java/ink/trmnl/android/data/TrmnlDeviceConfigDataStore.kt

@@ -377,7 +377,7 @@ class TrmnlDeviceConfigDataStore
          */
         suspend fun saveAccessToken(token: String) {
             context.deviceConfigStore.edit { preferences ->
-                preferences[ACCESS_TOKEN_KEY] = token
+                preferences[ACCESS_TOKEN_KEY] = token.trim()
             }
         }