chore(repo): stop tracking build artifacts; add README, license metadata, ruff config

Untrack iso/out/ (3.4 GB ISO), packaging/*/pkg/ trees, *.pkg.tar.zst and
tanin-icons/src/ (529 files) and ignore them going forward. Files stay on
disk. NOTE: history still carries ~13 GiB of old ISO blobs — needs a
git filter-repo pass (see README/report).

Also: first README.md, license + license-files in pyproject, minimal ruff
config, demo scripts moved to scripts/demo/.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -8,3 +8,15 @@ build/
 .mypy_cache/
 .pytest_cache/
 uv.lock
+
+# --- packaging: makepkg build artifacts ---
+packaging/*/pkg/
+packaging/*/src/
+*.pkg.tar.zst
+*.pkg.tar.zst.sig
+
+# --- ISO build output (multi-GB, regenerated per release) ---
+iso/out/
+
+# --- stray wheel builds ---
+*.whl