Dwarf caves in all modes: neutral dwarves guard a hoard and sometimes a rune chest; the rune forge tower; imps repair towers before claiming

- 1-4 cave slots by map size, 50% each (at least one); knight treasure caves only where a mission places them
- dwarves fight intruders near the cave, never chase far, heal at home, grow with distance and the player's army, never count for victory
- rune chest: one free rune forge tower (chain bolt to three more enemies), upgradeable for gold, sold once it comes back (next mission / free play at once), unbuilt ones carry over
- new tool (key N) shown in the tower menu while a rune tower can be built or upgraded

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

README.md

@@ -10,7 +10,7 @@ Dig out your underground realm, claim the portal to attract creatures, keep them
 - 3D isometric view with a freely rotatable and tiltable camera
 - Procedural pixel art, irregular cave walls, flickering torch light
 - CP437 text-mode style interface with the DINOBYTE bitmap font
-- Map sizes from 64×64 to 256×256 tiles (one portal per 64×64 tiles, guarded treasure caves on bigger maps)
+- Map sizes from 64×64 to 256×256 tiles (one portal per 64×64 tiles, dwarf caves with treasure and rune forge plans)
 - English and German (language files in `lang/`, easy to extend)
 
 See [DESIGN.md](DESIGN.md) for all design decisions and [CREDITS.md](CREDITS.md) for third-party assets.