fix(UXAssist): centralize mod-feature lifecycle to prevent duplicate execution

ModFeatureRegistry is a static class with shared collections accumulating
features from all mods. Dependent mods (CheatEnabler, UniverseGenTweaks)
each independently called InitAll/StartAll/OnInputUpdateAll/OnUpdateAll/
UninitAll, re-running lifecycle for ALL accumulated features including
other mods' — per-frame Update ran 2-3x (breaking CheatEnabler key toggles
to net no-ops), Init/Start/Uninit ran 2-3x (double RegisterExporter causing
save corruption, double SettingChanged subscriptions, double keybind
registration).

Fix:
- Init now runs eagerly at Discover/Register time (Awake-phase), preserving
  the original timing that keybind registration depends on (game's
  UIOptionWindow._OnCreate copies keybinds only after all plugins load)
- InitAll removed entirely
- StartAll/UninitAll/OnInputUpdateAll/OnUpdateAll made internal so only
  UXAssist (host, same assembly, no InternalsVisibleTo) can drive them
- Start deferred to UXAssist.Start (after all dependents' Awake complete;
  BepInEx runs all Awakes before any Start)
- Per-feature Started idempotency + per-frame Time.frameCount guards as
  defense-in-depth
- Dependent mods reduced to Discover-only in Awake

Document the Init/Start timing contract on IModFeature and
ModFeatureAttribute so future mods can rely on it.

UXAssist/UXAssist.cs

@@ -251,8 +251,11 @@ public class UXAssist : BaseUnityPlugin, IModCanSave
         object[] parameters = [_harmony];
         _compats?.Do(type => type.GetMethod("Init")?.Invoke(null, parameters));
 
+        // Register UXAssist's own features (Init runs eagerly here, preserving the original Awake timing
+        // that keybind registration relies on). Dependent mods register theirs during their own Awake
+        // phase. Start is deferred to UXAssist.Start below so that all dependents have registered before
+        // any feature starts.
         ModFeatureRegistry.Discover(Assembly.GetExecutingAssembly());
-        ModFeatureRegistry.InitAll();
 
         I18N.Apply();
     }
@@ -262,6 +265,8 @@ public class UXAssist : BaseUnityPlugin, IModCanSave
         MyWindowManager.InitBaseObjects();
         MyWindowManager.Enable(true);
 
+        // UXAssist is the sole lifecycle driver. All dependents have already registered (and initialized)
+        // their features during their Awake phase (BepInEx runs every plugin's Awake before any plugin's Start).
         ModFeatureRegistry.StartAll();
 
         _patches?.Do(type => type.GetMethod("Start")?.Invoke(null, null));