Add HTTPS support in dev mode and fix mobile layout issues

Generate self-signed certs for local HTTPS, add port 443 and full SSL
server block to dev nginx config, add Spotify redirect URI env var,
improve Spotify token error handling, and fix Chat/Steam mobile sizing.

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

backend/handlers/handle_spotify.go

@@ -21,7 +21,10 @@ func (store *Store) CompleteSpotifyAuth(ctx *gin.Context) {
 		return
 	}
 
-	services.SaveSpotifyToken(services.SPOTIFY_TOKEN_JSON_PATH, token)
+	if err := services.SaveSpotifyToken(services.SPOTIFY_TOKEN_JSON_PATH, token); err != nil {
+		ctx.String(http.StatusInternalServerError, "Failed to save token: %v", err)
+		return
+	}
 
 	client := spotify.New(store.SpotifyAuth.Client(c, token))
 

backend/services/spotify.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/zmb3/spotify/v2"
@@ -34,6 +35,10 @@ func SaveSpotifyToken(path string, tok *oauth2.Token) error {
 		Expiry:       tok.Expiry,
 	}
 
+	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
+		return fmt.Errorf("creating token directory: %w", err)
+	}
+
 	jsonBytes, err := json.MarshalIndent(data, "", "  ")
 	if err != nil {
 		return err