t_p1_round: Add round/match lifecycle system (RoundManager)

- New server/scripts/round/round_manager.gd with:
  - RoundPhase enum (WARMUP, PREP, LIVE, POST)
  - Round life cycle: warmup -> prep (15s) -> live (105s) -> post (8s)
  - Team elimination detection using entity->peer->team mappings
  - Time-expired round ending (default: CT wins)
  - Economy hooks: win money (250), loss money (900 escalating to 900), kill bonus (00)
  - All requested signals: round_phase_changed, round_started, round_ended, match_point, warmup_ended, round_economy_data

- Updated GameServer:
  - Creates and wires RoundManager in _ready()
  - Connects DamageProcessor.player_killed -> round tracking + elimination detection
  - Added peer_to_entity mapping for backwards entity lookup
  - Added RCON command handler (_on_rcon_command) for start_match/end_round

- Updated RCON command handler:
  - Added start_match and end_round to dispatch list and help text

server/scripts/rcon_command_handler.gd

@@ -57,7 +57,7 @@ func handle_command(cmd: String, args: PackedStringArray) -> String:
 			return _cmd_cvar_set(args)
 		"plugin":
 			return _cmd_plugin(args)
-		"say", "msg", "players", "changelevel", "kick", "ban", "unban", "exec":
+		"say", "msg", "players", "changelevel", "kick", "ban", "unban", "exec", "start_match", "end_round":
 			return _cmd_dispatch(cmd, args)
 		_:
 			return "Unknown command: '" + cmd + "'. Type 'help' for available commands.\\r\\n"
@@ -75,6 +75,8 @@ func _cmd_help(_args: PackedStringArray) -> String:
 		"  say <message>               Broadcast chat to all players",
 		"  msg <player> <message>      Send private message",
 		"  changelevel <map_name>      Load a new map",
+		"  start_match                 Start the match (exit warmup)",
+		"  end_round <team> [reason]   Force-end the current round",
 		"  kick <player> [reason]      Remove a player",
 		"  ban <player> [duration]     Ban a player from the server",
 		"  unban <player_or_steamid>   Remove a ban",