feat: formula-based ranking with optional AI, configurable score/pass-rate weights

Add scoreWeight and passRateWeight (0-10) to evaluation config for
configurable composite score formula. When ranking criteria text is
empty, triggerAutoRank uses pure formula ranking (no LLM calls).
When criteria text is present, AI-assisted ranking runs as before.

- Add FORMULA to RankingMode enum with migration
- Extract fetchCategoryProjects helper, add formulaRank service
- Update computeCompositeScore to accept configurable weights
- Add score/pass-rate weight sliders to ranking dashboard UI
- Mode-aware button labels (Calculator/formula vs Sparkles/AI)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types/competition-configs.ts

@@ -147,6 +147,10 @@ export const EvaluationConfigSchema = z.object({
 
   // Ranking (Phase 2) — per-criterion weights for AI ranking
   criteriaWeights: z.record(z.string(), z.number().min(0).max(10)).optional(),
+
+  // Ranking (Phase 3) — composite score formula weights
+  scoreWeight: z.number().min(0).max(10).default(5),
+  passRateWeight: z.number().min(0).max(10).default(5),
 })
 
 export type EvaluationConfig = z.infer<typeof EvaluationConfigSchema>