Honour forwarded headers only from MEALQUEST_TRUSTED_PROXY

Add internal/forwarded: parse the trusted proxy list (comma-separated IPs
and CIDRs, validated at load), resolve each request's client IP and scheme,
and expose them through context helpers. X-Forwarded-For and
X-Forwarded-Proto are honoured only when the TCP peer is trusted; the client
is the rightmost X-Forwarded-For address that is not a trusted proxy.
Malformed forwarded headers from a trusted peer get 400.

The router resolves every request first; a slog handler adds client_ip to
request-scoped log lines. The auth routes refuse requests whose resolved
scheme differs from MEALQUEST_PUBLIC_URL's, so a proxy that is not trusted
fails loudly instead of breaking Secure cookies. The OIDC redirect URI is
still built only from MEALQUEST_PUBLIC_URL.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/server/main.go

@@ -15,6 +15,7 @@ import (
 
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/auth"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/config"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/forwarded"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/frontend"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/server"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/store"
@@ -31,7 +32,7 @@ func main() {
 		os.Exit(1)
 	}
 
-	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
+	logger := slog.New(forwarded.LogHandler(slog.NewJSONHandler(os.Stdout, nil)))
 	if err := run(cfg, logger); err != nil {
 		logger.Error("server stopped", "error", err)
 		os.Exit(1)
@@ -68,7 +69,7 @@ func run(cfg config.Config, logger *slog.Logger) error {
 		return err
 	}
 
-	router, err := server.NewRouter(logger, version, authFlow, sessions, frontend.Assets())
+	router, err := server.NewRouter(logger, version, cfg.TrustedProxy, authFlow, sessions, frontend.Assets())
 	if err != nil {
 		return err
 	}
@@ -126,6 +127,7 @@ func logListening(logger *slog.Logger, cfg config.Config) {
 	logger.Info("listening",
 		"addr", cfg.HTTPAddr,
 		"public_origin", cfg.PublicOrigin(),
+		"trusted_proxy", cfg.TrustedProxy,
 		"data_dir", cfg.DataDir,
 		"version", version,
 	)