Initial release: full Arma 3 mod management toolchain

Pipeline: parse HTML presets, compare modlists, download from Caddy
file server, create junctions/symlinks to Arma 3 Server directory.
Includes update/sync flows, missing-mod reporting, OS compat layer,
shared config, dep checker, comprehensive test suite (71 tests).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config.template.json

@@ -0,0 +1,13 @@
+{
+  "server": {
+    "base_url": "https://your-caddy-server/arma3mods/",
+    "username": "your_username",
+    "password": "your_password"
+  },
+  "paths": {
+    "arma_dir":     "C:\\Path\\To\\Arma 3 Server",
+    "downloads":    "downloads",
+    "modlist_html": "modlist_html",
+    "modlist_json": "modlist_json"
+  }
+}