Phase 4-6: Quill editor, Lens viewer, Rigel context menu, CI, website

Phase 4 — native apps:
- quill/: text editor (monospace, double-buffered, find bar, undo, open/save)
- lens/: image viewer using imlib2 (zoom, pan, rotate, directory nav)
- wm/src/menu.c: launch quill instead of mousepad
- iso/docker/entrypoint.sh: add imlib2 package; install quill + lens binaries
- skykit/template/: developer app template demonstrating the SkyKit API

Phase 5 — file system and search:
- rigel/rigel.c: right-click context menu (open, open in quill, copy path,
  rename, trash, properties); Ctrl+F search/filter bar with name highlighting;
  F2 rename-in-place overlay; Delete key moves to trash

Phase 6 — distribution:
- .github/workflows/build-iso.yml: GitHub Actions CI that compiles all
  components and builds a bootable ISO on every tag push; creates a GitHub
  release with sha256 checksums

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

iso/docker/entrypoint.sh

@@ -38,6 +38,7 @@ ttf-liberation
 noto-fonts
 libxft
 fontconfig
+imlib2
 xf86-video-intel
 xf86-video-vesa
 mesa
@@ -242,6 +243,14 @@ fi
 if [[ -f "$SRC/rigel/rigel" ]]; then
     install -m755 "$SRC/rigel/rigel" "$AIROOTFS/usr/local/bin/rigel"
 fi
+# Quill text editor (compiled binary)
+if [[ -f "$SRC/quill/quill" ]]; then
+    install -m755 "$SRC/quill/quill" "$AIROOTFS/usr/local/bin/quill"
+fi
+# Lens image viewer (compiled binary)
+if [[ -f "$SRC/lens/lens" ]]; then
+    install -m755 "$SRC/lens/lens" "$AIROOTFS/usr/local/bin/lens"
+fi
 
 # ── 5. GTK theme ──────────────────────────────────────────────────────
 echo ">>> Installing GTK theme..."