feat: Scope3 SDK v2.0.0 - Persona-based API rebuild

[EmmaLouise2018]

Summary

Complete rebuild of the Scope3 SDK to match the live v2 Agentic Platform API. Replaces the old OpenAPI-generated code with a hand-crafted, persona-based TypeScript client.

• 3 persona-based APIs (buyer, brand, partner) via unified Scope3Client
• REST and MCP adapters with Bearer token auth and api_call tool
• 13 resource classes with full CRUD operations and input validation
• 3 campaign types: bundle, performance, audience with separate create/update endpoints
• Bundle-based product discovery workflow (create bundle → discover → add products → create campaign)
• skill.md parser with bundled fallback for all 3 personas
• CLI with --persona flag, config management, and all resource commands
• Webhook server with timing-safe auth, body validation, and size limits
• Security hardening: validateResourceId on all URL path params, sanitizeForLogging with depth limits and proto-key filtering, Promise caching for race conditions
• 225 tests across 14 suites, all passing
• Comprehensive docs: getting-started, buyer guide, brand guide, partner guide, CLI reference

Breaking Changes

• Package now requires persona in client config
• Auth uses Authorization: Bearer header (was x-scope3-api-key)
• Response envelope: { data, pagination, error } (was flat)
• Products are on bundles, not campaigns
• MCP uses single api_call tool (was per-resource tools)

Test plan

• npm run type-check — 0 errors
• npm run lint — 0 errors
• npm run build — clean
• npm test — 14 suites, 225 tests, all passing
• Two rounds of expert code review (code, security, TypeScript) with all critical/high/medium issues resolved
• Manual smoke test against staging: scope3 --persona buyer advertisers list
• Manual smoke test: scope3 --persona brand brands list
• Manual smoke test: scope3 --persona partner health