feat(server/membership): add ai_points plan policy fields

Introduces ai_points_monthly and ai_point_base_chars on the membership
plan policy, exposes them through TenantPlanAccess and MembershipInfo,
and seeds Pro with a 1500-point monthly allowance across the local,
server, and deploy configs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/shared/config/config_test.go

@@ -237,6 +237,12 @@ membership: {}
 	if pro.ArticleGeneration != 400 {
 		t.Fatalf("expected pro article generation 400, got %d", pro.ArticleGeneration)
 	}
+	if pro.AIPointsMonthly != 1500 {
+		t.Fatalf("expected pro ai points 1500, got %d", pro.AIPointsMonthly)
+	}
+	if pro.AIPointBaseChars != 1000 {
+		t.Fatalf("expected pro ai point base chars 1000, got %d", pro.AIPointBaseChars)
+	}
 	if pro.CompanyLimit != 2 {
 		t.Fatalf("expected pro company limit 2, got %d", pro.CompanyLimit)
 	}