Add Claude AI-powered response validation and update test model

Changes:
1. Update quick test to use gemma3:4b (was gemma2:2b)
   - Increased timeout to 60s for larger model

2. Implement Claude headless validation (validate.go)
   - Hybrid approach: simple checks first, then Claude validation ALWAYS runs
   - Claude validates response quality, coherence, relevance
   - Detects gibberish, errors, and malformed responses
   - Falls back to simple validation if Claude CLI unavailable
   - Verbose logging shows Claude validation results

3. Validation flow:
   - Step 1: Fast checks (empty response, token count)
   - Step 2: Claude AI analysis (runs regardless of simple check)
   - Claude result overrides simple checks
   - If Claude unavailable, uses simple validation only

4. Workflow improvements:
   - Remove useless GPU memory check step (server already stopped)
   - Cleaner workflow output

Benefits:
- Intelligent response quality validation
- Catches subtle issues (gibberish, off-topic responses)
- Better than hardcoded pattern matching
- Graceful degradation when Claude unavailable

test/config/quick.yaml

@@ -5,12 +5,12 @@ profiles:
   quick:
     timeout: 5m
     models:
-      - name: gemma2:2b
+      - name: gemma3:4b
         prompts:
           - "Hello, respond with a brief greeting."
         min_response_tokens: 5
         max_response_tokens: 100
-        timeout: 30s
+        timeout: 60s
 
 validation:
   gpu_required: true