feat(themes): ✨ add theme installer

[amd989]

Summary

• Add lcd4linux-ax206-themes as a separate optional Debian package containing 39 pre-built themes, 5 TrueType font families, and the new lcd4linux-theme CLI
• Add WorkingDirectory=/usr/share/lcd4linux to the systemd service so relative paths in theme configs resolve correctly out of the box
• Add lcd4linux-theme CLI for listing, applying, and tracking themes without manual config editing

Details

Previously, installing the package gave users a bare text-only config with no themes available. Using a theme required manually locating the config, background image, and fonts, copying everything into place, and hand-editing all paths to be absolute. because lcd4linux resolves resource paths relative to its working directory.

This PR fixes that end-to-end:

New package: lcd4linux-ax206-themes
Keeps themes and fonts (~17MB) out of the core package for users who don't need them. Depends on lcd4linux-ax206.

lcd4linux-theme CLI (/usr/bin/lcd4linux-theme):

lcd4linux-theme list                    # list all 39 themes with descriptions
sudo lcd4linux-theme apply SimpleBlue   # apply a theme, backs up current config
lcd4linux-theme current                 # show active theme

apply creates a timestamped backup of the existing config before overwriting, and restarts the service if it is running.

Systemd service fix
WorkingDirectory=/usr/share/lcd4linux is the key change that makes all theme configs work as-is — no path editing required. The default dpf_320x240.conf is unaffected (it uses only the built-in bitmap font).

Bugfix
Fixed a pre-existing typo in themes/SimpleOrangeFall/dpf_simpleorangefall.conf where the background image path referenced SimpleOarngeFall instead of SimpleOrangeFall, causing a silent render failure.

Files changed

File	Change
lcd4linux-theme	New theme management CLI script
debian/control	Add lcd4linux-ax206-themes package stanza
debian/lcd4linux-ax206-themes.install	New install list for themes package
debian/lcd4linux-ax206.dirs	Ensure /usr/share/lcd4linux exists in main package
debian/lcd4linux-ax206.service	Add WorkingDirectory, update error message
debian/rules	Add chmod 0755 for the script
themes/SimpleOrangeFall/dpf_simpleorangefall.conf	Fix background path typo
themes/README.md	Document lcd4linux-theme usage
README.md	Document themes package and CLI
wiki/theme_management.md	New wiki page
wiki/ax206_features.md	Add Theme Management section
wiki/Home.md, wiki/_Sidebar.md	Add navigation links

Test plan

• lcd4linux-theme list prints all 39 themes with descriptions
• sudo lcd4linux-theme apply SimpleBlue copies config, creates backup, restarts service
• lcd4linux-theme current shows SimpleBlue after apply
• Re-applying a theme creates a new timestamped backup
• dpkg-buildpackage produces both lcd4linux-ax206 and lcd4linux-ax206-themes debs
• lcd4linux-ax206 contains /usr/share/lcd4linux/ (empty dir) but not themes/fonts
• lcd4linux-ax206-themes contains themes, fonts, and lcd4linux-theme binary
• Systemd service starts successfully with WorkingDirectory set; theme background and fonts render correctly
• Default dpf_320x240.conf still works on a system with only lcd4linux-ax206 installed (no themes package)