Add auto-incrementing version display to web UI footer

Exposes GET /version endpoint in the web container (reads APP_VERSION env var).
CI computes the version as 1.0.<git-commit-count> and passes it via --build-arg at build time.
Both index.html and cv-matcher/index.html show the version in the footer via a JS fetch.
docker-compose passes APP_VERSION through to the running container.

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

web/Program.cs

@@ -14,6 +14,9 @@ var app = builder.Build();
 
 app.UseMiddleware<SiteModeMiddleware>();
 
+app.MapGet("/version", (IConfiguration config) =>
+    Results.Json(new { version = config["APP_VERSION"] ?? "unknown" }));
+
 // Static site
 app.UseDefaultFiles();
 app.UseStaticFiles();