feat(ui-design): add memory check mechanism to workflow commands

Add Phase 0.1/1.1 memory check to all UI design workflow commands to skip
execution when outputs already exist. This optimization dramatically reduces
redundant execution time from minutes to <1 second.

Changes:
- extract.md: Check for style-cards.json, skip Phase 0.5-3 if exists
- consolidate.md: Check for style-1/design-tokens.json, skip Phase 2-6
- generate.md: Check for compare.html, skip Phase 1.5-4
- update.md: Check for current design run in synthesis-spec, skip Phase 2-5

Benefits:
- >99% time reduction for repeated workflow execution
- Automatic cache detection without manual flags
- Clear reporting of skipped phases

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.claude/commands/workflow/ui-design/generate.md

@@ -104,6 +104,16 @@ FOR style_id IN range(1, style_variants + 1):
 IF --session: synthesis_spec = Read(.workflow/WFS-{session}/.brainstorming/synthesis-specification.md)
 ```
 
+### Phase 1.1: Memory Check (Skip if Already Generated)
+
+```bash
+# Check if compare.html exists in memory
+IF exists("{base_path}/prototypes/compare.html"):
+    REPORT: "✅ UI generation already complete (found in memory)"
+    REPORT: "   Skipping: Phase 1.5-4 (Layout Planning, Token Conversion, Template Generation, Prototype Instantiation, Preview Verification, Completion)"
+    EXIT 0
+```
+
 ### Phase 1.5: Target-Specific Layout Planning
 
 ```bash