ML-158: force single-line log output in production

Three-layer architecture:
- Logster v2 handles HTTP request and LiveView socket telemetry in logfmt format
- Custom formatter as safety net escaping any remaining embedded newlines
- Config flag (single_line_logging) gating Logster attachment to prod only

Dev environment retains multi-line format for readability.

config/config.exs

@@ -97,6 +97,8 @@ config :tailwind,
     cd: Path.expand("..", __DIR__)
   ]
 
+config :music_library, :single_line_logging, false
+
 # Configures Elixir's Logger
 config :logger, :default_formatter,
   format: "$time $metadata[$level] $message\n",