Redesign skill system with upgrade trees and tier progression

Major changes:
- Created docs/skills.md with comprehensive skill system documentation
- Rewrote skill-evolution.ts with new upgrade tree structure:
  - Upgrades organized in branching paths with prerequisites
  - Each choice can lead to upgraded versions at future milestones
  - Support for upgrade children and requirement chains
- Added getBaseSkillId and generateTierSkillDef helper functions
- Fixed getFloorElement to use FLOOR_ELEM_CYCLE.length
- Updated test files to match current skill definitions
- Removed tests for non-existent skills

Skill system now supports:
- Levels 1-10 for most skills, level 5 caps for specialized, level 1 for research
- Tier up system: Tier N Level 1 = Tier N-1 Level 10 in power
- Milestone upgrades at levels 5 and 10 with branching upgrade trees
- Attunement requirements for skill access and tier up
- Study costs and time for leveling

worklog.md

@@ -633,3 +633,40 @@ 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
+
+- **Fixed tier-up upgrade reset in tierUpSkill()**:
+  - Root cause: `tierUpSkill()` was setting new tier's upgrades to empty array `[]`
+  - When tiering up, all previous tier's upgrades were lost
+  - Now copies current tier's upgrades to the new tier
+  - Example: Tier 1's L5/L10 upgrades persist when becoming Tier 2
+
+- **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
+- Upgrades now carry over when tiering up to the next tier
+- Players can safely select upgrades at both milestones across all tiers
+- Summoned golems now visible in Spire tab during combat
+- Lint passes, pushed to git (e2671d7)