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).

config.yml.example

@@ -0,0 +1,44 @@
+# gitea-svn-mirror configuration
+# Full reference: see README.md
+
+data_dir: /var/svn-mirror
+
+mirrors:
+  - id: my-project
+    enabled: true
+
+    # ── SVN remote ──────────────────────────────────────────
+    svn:
+      url: https://svn.example.com/svn/myproject
+      layout: std              # "std" or "custom"
+      # For non-standard layout:
+      # layout: custom
+      # trunk: trunk
+      # branches: branches
+      # tags: tags
+
+    # ── Gitea integration ───────────────────────────────────
+    gitea:
+      owner: myorg
+      repo: myproject
+
+      # Path to Gitea's on-disk bare repos.  Required for
+      # push_to_gitea, fetch_from_gitea, and the webhook flow.
+      # Typical locations:
+      #   Gitea binary → /var/lib/gitea/data/repositories
+      #   Gitea Docker → /data/git/repositories
+      #   git user     → /home/git/repositories
+      repos_path: /var/lib/gitea/data/repositories
+
+      # Webhook receiver (used by `webhook` command)
+      webhook_secret: "change-me-to-a-random-secret"
+      webhook_host: "0.0.0.0"
+      webhook_port: 8080
+
+    # ── Author mapping (SVN username → Git author) ──────────
+    authors:
+      "john": "John Doe <john@example.com>"
+      "jane": "Jane Doe <jane@example.com>"
+
+    # ── SVN poll interval (seconds) ─────────────────────────
+    sync_interval: 120