Code Farm economy rebalance: market saturation, infrastructure/defense/cosmetics, mastery track, secondary leaderboards, admin eras, underdog bonus and weekly contracts

Every purchase/upgrade path (new and pre-existing) is now race-safe against concurrent requests via atomic conditional SQL updates.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

devplacepy/templates/_game_defense.html

@@ -0,0 +1,13 @@
+<div class="shop-row">
+    <div class="shop-info">
+        <strong>Defense: {{ farm.defense_tier_name }} (level {{ farm.defense_level }})</strong>
+        <span>{% if farm.defense_upkeep_daily %}Costs {{ farm.defense_upkeep_daily }}c/day upkeep - unpaid protection decays a level.{% else %}No upkeep at level 0.{% endif %}</span>
+    </div>
+    {% if farm.defense_next_cost %}
+    <form method="post" action="/game/defense/upgrade" data-game-action="defense">
+        <button type="submit" class="btn btn-sm btn-primary">Upgrade ({{ farm.defense_next_cost }}c)</button>
+    </form>
+    {% else %}
+    <span class="perk-maxed">Maxed</span>
+    {% endif %}
+</div>