perf: pin quality tests to Opus, add --retry 2 and test:e2e:fast tier

~10 quality-sensitive tests (planted-bug detection, design quality judge,
strategic review, retro analysis) explicitly pinned to Opus. ~30 structure
tests default to Sonnet for 5x speed improvement.

Added --retry 2 to all E2E scripts for flaky test resilience.
Added test:e2e:fast script that excludes 8 slowest tests for quick feedback.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/skill-e2e-qa-bugs.test.ts

@@ -100,6 +100,7 @@ CRITICAL RULES:
       timeout: 300_000,
       testName: `qa-${label}`,
       runId,
+      model: 'claude-opus-4-6',
     });
 
     logCost(`/qa ${label}`, result);