Fix #69: install Plymouth ourselves instead of relying on Armbian's flag

[eliasbakken]

Problem

Fixes #69. No splash screen during boot on Recore.

Root cause

recore.csc's extension_finish_config__enable_plymouth() hook (which set PLYMOUTH=yes) was commented out and never actually ran. Not a BUILD_MINIMAL conflict as first suspected while investigating - just dead code that silently did nothing. Plymouth was never installed at all.

Fix

Rather than re-enable Armbian's own PLYMOUTH/armbian-plymouth-theme mechanism, install plymouth ourselves via a new install_components script, the same way Rebuild already installs Klipper/Moonraker/weston/etc. Avoids depending on Armbian's internal variable semantics, which is exactly what broke this in the first place and could break again on a future Armbian bump.

• New install_components/plymouth.sh: installs plymouth + plymouth-themes, wires Recore's watermark into the spinner theme's logo (moved from the dead armbian/watermark.png path, which rebuild.sh was copying into a package we never actually build), and re-centers it (the theme's default WatermarkVerticalAlignment of .96 puts it right at the bottom of the screen).
• Wired into fluidd/mainsail/octoprint (not barebone - no display).
• weston.service now has After=plymouth-quit-wait.service. Found while testing: without it, weston can race Plymouth's DRM handoff and come up with a broken/black display even though the process itself reports healthy - a manual restart recovers it, but shouldn't be needed. Only affects octoprint (toggle.sh); fluidd/mainsail use KlipperScreen over X11, which was confirmed clean on the same test.

Rotation (panel_orientation) is handled separately by a matching change to Reflash's rotate-screen (new PLYMOUTH place).

Test plan

• Validated live on real hardware before formalizing into a build script (installed plain plymouth+plymouth-themes, confirmed the splash renders on this kernel/hardware at all)
• Built rebuild-fluidd and rebuild-octoprint locally with these changes and flashed both to real hardware
• Fluidd: splash + centered watermark confirmed, KlipperScreen comes up clean afterward (no ordering fix needed there)
• Octoprint: splash + centered watermark confirmed; without the weston.service ordering fix, hit the black-screen race; with it, Toggle comes up clean without a manual restart
• Rotation confirmed correct end-to-end together with the matching Reflash change

🤖 Generated with Claude Code