feat(eligibility-rules): implement deterministic community eligibility rules engine

Implements issue #384. Adds the @guildpass/eligibility-rules package at
packages/eligibility-rules with:

- EligibilityRule discriminated union (equals, exists, in, gte, lte,
  all, any, not)
- parseEligibilityRule: validates untrusted input against the rule
  grammar with configurable depth and node-count limits
- evaluateEligibilityRule: evaluates a rule tree against a caller-
  supplied facts object, returning a structured eligibility decision
- Dot-separated fact path resolution that safely handles missing
  segments and null mid-path values
- explain mode that collects stable machine-readable denial reasons
- Configurable and exported DEFAULT_ELIGIBILITY_RULE_LIMITS
- No database, HTTP or external runtime dependencies
- 90 unit tests covering all predicates, nesting, missing fields,
  type mismatches, boundary cases, depth/node limits and explain mode

pnpm typecheck, pnpm build and pnpm test all pass across the monorepo.

Closes #384

Author: godwinishaku506-hub

packages/eligibility-rules/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "@guildpass/eligibility-rules",
+  "version": "2.0.0",
+  "private": true,
+  "type": "module",
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js"
+    }
+  },
+  "scripts": {
+    "build": "tsc -p tsconfig.json",
+    "typecheck": "tsc -p tsconfig.json --noEmit",
+    "test": "node --test dist/**/*.test.js"
+  }
+}