feat: comprehensive balance pass (#239)

- fix: boss signature chain maintained through fight results (#148)
- fix: militia cost curve smoothed (100g -> 65g) (#145)
- fix: crystal_shard buffed to epic tier (1.65x/1.2x -> 1.9x/1.3x) (#144)
- fix: click_power recipe ceiling raised and z13-18 progression smoothed (#142)
- close: elder_bark_shield, void_fragment_amulet, soul_bound_catalyst already at target values (#143)

apps/web/src/context/gameContext.tsx

@@ -1496,11 +1496,20 @@ export const GameProvider = ({
               });
 
               /*
-               * Boss fight modifies server state; clear stale signature so
-               * the next pre-save or auto-save does not send a mismatched one.
+               * Boss fight modifies server state; update signature chain so
+               * the next pre-save or auto-save sends the correct token.
                */
-              signatureReference.current = null;
-              localStorage.removeItem("elysium_save_signature");
+              if (result.signature === undefined) {
+                signatureReference.current = null;
+                localStorage.removeItem("elysium_save_signature");
+              } else {
+                signatureReference.current = result.signature;
+                localStorage.setItem(
+                  "elysium_save_signature",
+                  result.signature,
+                );
+              }
+              lastSaveReference.current = Date.now();
               setAutoBossLastResult({
                 at:       Date.now(),
                 bossName: bossName,
@@ -2177,6 +2186,14 @@ export const GameProvider = ({
         }
         return applyBossResult(previous, bossId, result);
       });
+      if (result.signature === undefined) {
+        signatureReference.current = null;
+        localStorage.removeItem("elysium_save_signature");
+      } else {
+        signatureReference.current = result.signature;
+        localStorage.setItem("elysium_save_signature", result.signature);
+      }
+      lastSaveReference.current = Date.now();
       setBattleResult({ bossName: boss.name, result: result });
     } catch (error_: unknown) {
       const bossErrorMessage