Add external Challenge Prisma client for Opportunities

[jmgasper]

Summary

• publish a stable external Prisma client package for opportunities-api-v6
• keep Prisma 7 adapter setup and schema handling inside the owning API
• expose allow-listed PostgreSQL driver settings for bounded connection acquisition, client query, and server statement timeouts
• document and test the supported factory contract
• add role-specific member challenge search through memberId plus exact UUID resourceRoleId
• apply the role constraint in the resource-backed candidate view before challenge filters, global sort, count, and pagination
• preserve all existing caller whitelist, group, and task visibility rules; the member query only narrows results and never grants access
• extend MemberChallengeAccess and its migration with roleId (migration must deploy before this service version)

Validation

• focused ChallengeService regressions: 5 passed, covering role omission, anonymous task visibility, validation, legacy-ID composition, and global status sort/count/pagination
• pnpm test:external-client (3 passed)
• pnpm lint
• pnpm build
• isolated PostgreSQL migration/view integration check passed for member/role challenge selection
• e2e runner currently stops before test discovery at the repository-wide Chai 6 / chai-http plugin import incompatibility in test/e2e/attachment.api.test.js:16
• full unit suite remains red in unrelated existing suites/environment state; the focused changed-path regressions pass

Latest head: c06ab1f284e178bbab3c9e422b936a2e0709c27b

Part of the Topcoder Opportunities v6 experience.