fix(boot): fix black screen on monitor, stop log spam on console

- Add console=tty0 so VGA display gets kernel output (was serial-only)
- Change loglevel=7→3 (debug→errors only)
- Add quiet to suppress verbose kernel boot messages
- journald: ForwardToConsole=no so service logs don't flood tty1

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/overlay/etc/systemd/journald.conf.d/bee.conf

@@ -0,0 +1,4 @@
+[Journal]
+# Do not forward service logs to the console — bee-tui runs on tty1
+# and log spam makes the screen unusable on physical monitors.
+ForwardToConsole=no