Rename iron to metal, add mining and recruitment

- Updated CLI, README and documentation to use `--starting-metal` with
  `--starting-iron` retained as an alias.
- Introduced `Resources` struct and constants for wood delivery and mine
  production.
- Added new structures `Mine` and `MineConstruction` with cost,
  production
  and cancel logic.
- Implemented building view for constructing mines and recruitment view
  for spawning miners.
- Extended keybindings with `Building` and `Recruitment` actions and
  updated
  action availability logic.
- Modified game state, board, units and UI widgets to handle metal
  resources
  and new construction mechanics.
- Updated tests and increased total test count to 82, covering
  resources,
  construction, recruitment and context‑aware keybindings.

src/app/state.rs

@@ -1,7 +1,7 @@
 use crate::{
   app::states::{
     MainMenuState, PerkDecksState, SettingsState, SkillsConfigState, SkirmishState,
-    skirmish_states::BoardState,
+    skirmish_states::{BoardState, Resources},
   },
   cli::Cli,
 };
@@ -36,6 +36,10 @@ impl GameStates {
         ),
         side_panel: false,
         turn_counter: 0,
+        player_resources: Resources::new(args.starting_wood, args.starting_metal),
+        enemy_resources: Resources::new(args.starting_wood, args.starting_metal),
+        building_view: false,
+        recruitment_view: false,
       },
       perk_decks: PerkDecksState {
         id: 2,
@@ -52,7 +56,7 @@ impl GameStates {
         game_mode: args.game_mode.clone(),
         perk_deck: args.perk_deck.clone(),
         starting_wood: args.starting_wood.clone(),
-        starting_iron: args.starting_iron.clone(),
+        starting_metal: args.starting_metal,
         supply_limit: args.supply_limit.clone(),
         xp_modifier: args.xp_modifier.clone(),
         skill_points_limit: args.skill_points_limit.clone(),