Implement versiond M1: inotify monitor, versioning, diff, restore, systemd install

FastAPI service on 127.0.0.1:9922 that monitors user-chosen directories
with pruned inotify watches, stores versions in a local content-addressed
spool indexed in SQLite, coalesces bursts (first + last), and offers
history, diff and dry-run-first bulk restore. Includes a CLI with a
systemd user unit installer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,6 @@
+.venv/
+__pycache__/
+*.egg-info/
+.pytest_cache/
+build/
+dist/