Campaign mission system: 20 mission definitions, goals, unlocks, carry-over

- campaign.rs: missions as key data (size, rivers, fortresses, goals, waves, time limit, gifts);
  start_mission builds the map with the generator; tools unlock step by step; the strongest
  5 creatures and 20% of the gold are carried into the next mission; campaign progress type
- Map generator options (portals, treasure caves, hero gate) and meandering rivers with
  knight bridges
- Mission goals: shards, gate of the order, all knights, vault loot, knight towers, waves;
  time limits; waves and gate defenders only where the mission wants them
- Locked tools are shown dark and cannot be chosen; HUD shows gate/waves/time only when used
- Fix: patrol routes no longer start on tower spots
- Tests: every mission builds, its goals are possible, wave heroes reach the core

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

lang/en.lang

@@ -424,3 +424,10 @@ msg.bridge_torn = The knights have torn down one of your bridges!
 job.tear_bridge = Tearing down a bridge
 job.patrol = On patrol
 job.guard = On guard
+
+# campaign
+msg.mission_start = Mission: {0}
+msg.mission_won = Mission accomplished!
+msg.time_up = Time is up - the knights have secured their treasures.
+hud.time_left = Time
+msg.tool_locked = This is not available yet in this mission.