Add Connect 4 multiplayer game server

Real-time two-player Connect 4 using Via framework with:
- Game creation and invite links
- SSE-based live updates for both players
- Win detection with animated highlighting
- Session-based nickname persistence

go.mod

@@ -0,0 +1,19 @@
+module github.com/ryanhamamura/c4
+
+go 1.25.4
+
+require (
+	github.com/go-via/via-plugin-picocss v0.1.1
+	github.com/ryanhamamura/via v0.2.3
+)
+
+require (
+	github.com/CAFxX/httpcompression v0.0.9 // indirect
+	github.com/alexedwards/scs/v2 v2.9.0 // indirect
+	github.com/andybalholm/brotli v1.2.0 // indirect
+	github.com/go-via/via v0.1.4 // indirect
+	github.com/klauspost/compress v1.18.0 // indirect
+	github.com/starfederation/datastar-go v1.0.3 // indirect
+	github.com/valyala/bytebufferpool v1.0.0 // indirect
+	maragu.dev/gomponents v1.2.0 // indirect
+)