ci: repoint desktop build off the deleted slopsmith org

The slopsmith org was deleted in the DMCA relaunch; core + plugins now
live under the private got-feedback org. Repoint the whole build:

- core clone (nightly.yml, build-common.sh) -> got-feedback/feedback,
  authenticated via GH_CLONE_TOKEN (a PAT with read on the private org;
  threaded through build.yml/nightly.yml/release.yml). Local builds
  without it fall back to the git credential helper.
- bundled-plugin list -> got-feedback/feedback-plugin-*, pruned to the
  set that exists in the org: drops the removed extraction plugins
  (profileimport, tones, sloppak-converter) and not-yet-rehomed ones
  (nam-rig-builder, tabimport); 34 plugins bundled.
- dirname derivation strips the new feedback-plugin- prefix.
- ghcr image -> ghcr.io/got-feedback/feedback; VERSION-sync dispatch
  -> got-feedback/feedback; soundfont + update FEED_URL + docs ->
  got-feedback/feedback-desktop.

Two prerequisites remain (owner-only): set the GH_CLONE_TOKEN secret,
and re-upload the soundfonts-v1 release assets to feedback-desktop.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/bundle-slopsmith.sh

@@ -32,7 +32,7 @@ if [ -z "$SLOPSMITH_DIR" ] || [ ! -d "$SLOPSMITH_DIR" ]; then
     echo "  \$SLOPSMITH_DIR (unset)" >&2
     echo "  $PROJECT_DIR/../slopsmith" >&2
     echo "  $HOME/Repositories/slopsmith" >&2
-    echo "Clone it with: git clone https://github.com/slopsmith/slopsmith.git ../slopsmith" >&2
+    echo "Clone it with: git clone https://github.com/got-feedback/feedback.git ../slopsmith" >&2
     exit 1
 fi