Fix upgrade reset bugs: milestone merging and tier-up carryover

- Fixed commitSkillUpgrades() to preserve upgrades from other milestones
  (selecting L10 upgrades no longer resets L5 selections)
- Fixed tierUpSkill() to carry over upgrades from previous tier
  (tier 2 now starts with tier 1's upgrades intact)
- Added summoned golems display to SpireTab with stats and progress bars

worklog.md

@@ -633,3 +633,33 @@ Stage Summary:
 - UI for selecting and managing golems
 - Documentation updated
 - Lint passes
+
+---
+Task ID: 28
+Agent: Main
+Task: Fix level upgrade reset loop bug and add golem display to SpireTab
+
+Work Log:
+- **Fixed upgrade reset bug in commitSkillUpgrades()**:
+  - Root cause: `commitSkillUpgrades()` was replacing ALL upgrades for a skill instead of merging by milestone
+  - When selecting level 10 upgrades, it would wipe out level 5 selections (and vice versa)
+  - Added optional `milestone` parameter (5 | 10) to the function
+  - When milestone is specified, the function now:
+    - Keeps existing upgrades from OTHER milestones
+    - Only replaces upgrades for the CURRENT milestone
+  - Updated type definition in GameStore interface
+  - Updated SkillsTab.tsx to pass `upgradeDialogMilestone` when committing
+
+- **Added summoned golems display to SpireTab**:
+  - Imported GOLEMS_DEF and helper functions
+  - Added Mountain icon import
+  - Added "Active Golems" card that appears when golems are summoned
+  - Shows each golem's name, damage, attack speed, and armor pierce
+  - Displays attack progress bar when climbing
+  - AOE badge for golems with area attacks
+
+Stage Summary:
+- Level 5 and level 10 upgrades no longer reset each other
+- Players can safely select upgrades at both milestones
+- Summoned golems now visible in Spire tab during combat
+- Lint passes, dev server running