Add ore level support and unify text rendering

Introduce a numeric `level` field for `BaseBuilding` and `Ore`, update
their
constructors and `get_level` implementations, and increase the default
ore
amount to the new maximum. Extend the `Structure` and `Unit` traits with
`base_text` and `text` methods, add `is_unit` to `Units`, and adjust the
`Structures` enum to delegate text rendering. Refactor `SidePanelWidget`
to
use the unified trait methods, removing duplicated rendering code.
Update
`BoardState` to create ore structures with an initial level of 1.

src/app/states/skirmish_states/structures/structures_enum.rs

@@ -2,7 +2,7 @@ use crate::app::states::skirmish_states::{
     Players,
     structures::{BaseBuilding, Ore, Stone, Structure, Tunnel},
 };
-use ratatui::style::Color;
+use ratatui::{style::Color, text::Line};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Structures {
@@ -56,4 +56,8 @@ impl Structure for Structures {
     fn get_owner(&self) -> Players {
         self.structure().get_owner()
     }
+
+    fn text(&self) -> Vec<Line<'_>> {
+        self.structure().text()
+    }
 }