feat(research): add competitive opportunities

[iannuttall]

Summary

• add a bounded provider-neutral competitive opportunity report across keyword discovery, live SERPs, Ahrefs Domain Rating, and optional link summaries
• preserve source coverage, costs, failures, cache state, market semantics, and evidence references without turning provider metrics into a feasibility score
• register the report across CLI and MCP discovery, agent guidance, evals, documentation, telemetry, and the public package
• balance competitor enrichment across each keyword’s highest current results and retain completed snapshots after later provider timeouts

Verification

• pnpm build
• pnpm typecheck
• pnpm test
• pnpm lint
• pnpm pack --dry-run
• maximum competitive-opportunities resource harness under a 192 MiB heap
• live Semrush, DataForSEO, and Ahrefs validation using private local test data
• tracked and staged source scans confirmed no private domains, credentials, or provider payloads are included