feat: add 5 audio + utility Selkies images (ardour, lmms, lollypop, qdirstat, doublecommander)

[JoshuaAFerguson]

Summary

Cleanest batch yet — all 5 are single-line apt installs, no debug surprises.

Image	Category	Audio	Mem req/lim
ardour-selkies	Audio & Video	on	4 / 8 Gi
lmms-selkies	Audio & Video	on	4 / 4 Gi
lollypop-selkies	Audio & Video	on	1 / 2 Gi
qdirstat-selkies	Utilities	off	1 / 2 Gi
doublecommander-selkies	Utilities	off	1 / 2 Gi

Notes

• doublecommander: picked the Qt5 build (`doublecmd-qt`) over the GTK2 build (`doublecmd-gtk`) — Qt5 integrates better with the base's libs and the GTK2 version is increasingly legacy.
• LMMS is a NEW addition (no legacy entry). The other 4 replace existing pending-migration templates.

Removed legacy KasmVNC templates

`audio-video/ardour.yaml`, `audio-video/lollypop.yaml`, `utilities/qdirstat.yaml`, `utilities/doublecommander.yaml`.

Local verification skipped (Docker disk)

All 5 packages confirmed in Ubuntu noble apt-cache:
```
ardour - the digital audio workstation
lmms - Linux Multimedia Studio
lollypop - modern music player
qdirstat - Qt-based directory statistics
doublecmd-qt - twin-panel (commander-style) file manager (Qt5)
```

Test plan

• All 5 packages confirmed in apt
• CI matrix builds all 5 successfully
• CI `Validate Template Manifests` accepts all 5 new manifests
• After merge: all 5 publish to ghcr.io

Catalog progress

After this lands: 55 published Selkies-native images. ~17 templates remain pending-migration.

Remaining tail

• Communication tail (pidgin, ferdium, webcord, altus) — Electron + apt mix
• Desktop environments (kali-linux, webtop variants) — heavyweight, different approach
• Music streaming (spotube — Spotify-like with Spotify integration via Yandex Music API; vendor .deb)
• Misc (gitqlient, bitcoin-knots, calligra, mullvad-browser, msedge, ungoogled-chromium, ferdium tail, dogwalk gaming, gzdoom, luanti, mame, flycast, xemu, steamos, kali, webtops, ...)