Rivers and bridges: water and lava tiles, bridge tool, burning in lava

- New tile kinds (appended for the savegame codec): water, lava, wooden bridge, stone bridge, core shard
- Sunken river beds with banks, bridge decks with rails, lava glow and lights
- Bridge tool (key U, rooms category): bridges grow from own ground, 30 gold/tile over water, 75 over lava
- Selling a bridge drops the units on it into the river (water: swim to the bank, lava: burn)
- Cannon blasts and punches knock units back; into lava = burnt (heroes still pay their bounty)
- Heroes cannot path through rivers; texts EN/DE; tests for bridges and lava

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

lang/en.lang

@@ -146,7 +146,7 @@ help.k_slap = Shift+Left      Hand: backhand own units, punch heroes on your gro
 help.k_pan = Right drag      Move the map (also WASD/arrows, screen edge)
 help.k_rot = Middle drag     Rotate and tilt the camera (also Q/E, R/F)
 help.k_zoom = Mouse wheel     Zoom
-help.k_tools = 1-9,0,X,V,K,J,B,C,T  Select tool
+help.k_tools = 1-9,0,X,V,K,J,B,C,T,U  Select tool
 help.k_misc = P / Space       Pause      M  Sound on/off   +/-  Volume
 help.k_misc2 = G               Tile outlines on/off     H  This help
 help.s1 = 1. Dig to the portal and let your Pit Imps claim it.
@@ -384,3 +384,21 @@ help.t_long = Long press: information about the spot; hand: drop the units there
 help.t_double = Double tap with the hand: backhand own units, punch heroes on your ground
 help.t_tools = Toolbar: categories open a row of tools; the menu button opens the pause menu
 help.start_touch = Tap to start
+
+# rivers and bridges
+tool.bridge.label = Bridge
+tool.bridge.name = Build Bridge
+tool.bridge.desc = Builds a bridge over water or lava. Drag from your own ground across the river; the bridge grows tile by tile from your territory.
+cost.bridge = {0} gold/tile over water, {1} over lava
+hint.bridge_where = Bridges must start at your own ground: drag from your territory across the river.
+hint.bridge_river = Bridges can only be built over water or lava.
+msg.hero_burned = A {0} fell into the lava! +{1} gold.
+msg.creature_burned = Your {0} fell into the lava.
+tile.water = Underground river
+tile.water_info = Nobody can wade through it. Build a bridge.
+tile.lava = Lava
+tile.lava_info = Whatever falls in burns. Stone bridges cross it.
+tile.bridge = Wooden bridge
+tile.lavabridge = Stone bridge
+tile.shard = Shard of your soul core
+tile.shard_info = Claim this chamber to take the shard back.