feat: initial import — SVN↔Git bi-directional mirror for Gitea

Server-side sidecar daemon. Uses own SQLite mapping table (not git svn)
so Git commit hashes never change. Pure Python, zero framework deps.

Includes:
- SVN→Git sync engine with nested-directory tree reconstruction
- Git→SVN push with author mapping and working-copy management
- Branch/tag sync (svn copy → git branch/tag and reverse)
- Gitea integration (on-disk push/fetch, webhook receiver)
- Reconciliation tool for divergence recovery (assess + auto-fix)
- Full end-to-end regression test (bash, 34 checks)
- systemd unit and deployment docs

Only external dependency: PyYAML (config parsing).

svn_mirror/__main__.py

@@ -0,0 +1,3 @@
+from .cli import main
+
+main()