feat: add download/clone tracking and PyPI publishing

- Add shields.io badges to docs front page (desktop downloads, PyPI
  installs, git clones, GitHub stars)
- Add daily GitHub Action to accumulate git clone traffic data
- Add PyPI publish workflow triggered on tags and releases
- Add PyPI metadata (license, authors, classifiers, URLs) to pyproject.toml

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/clone-stats/badge.json

@@ -0,0 +1,7 @@
+{
+  "schemaVersion": 1,
+  "label": "Git Clones",
+  "message": "0",
+  "color": "green",
+  "namedLogo": "git"
+}

.github/clone-stats/clone-data.json

@@ -0,0 +1,5 @@
+{
+  "total_clones": 0,
+  "last_updated": "",
+  "daily": {}
+}