docs(content): add Multi-Source Search skill

[denial123789]

Summary

Adds one source-backed skill entry for Multi-Source Search, a portable research and fact-checking workflow from sandbaseai/sandbase-skills.

The entry documents:

• multi-provider retrieval and claim cross-validation
• evidence provenance, derivative-source detection, and confidence scoring
• a six-search/six-page default budget with early stopping
• optional evidence-ledger JSON and its offline Python validator
• Claude Code, Codex, Cursor, Gemini CLI, and generic Agent Skills compatibility
• explicit network, prompt-injection, local-write, provider-data, credential, and retention considerations

Source and installation

• Canonical skill: https://github.com/sandbaseai/sandbase-skills/tree/main/research/multi-source-search
• Install: npx skills add sandbaseai/sandbase-skills --skill multi-source-search
• License: Apache-2.0

Validation

• pnpm install --frozen-lockfile
• pnpm validate:content:strict — passed (1,389 content files; only 24 pre-existing warnings in unrelated entries)
• git diff --check — passed

This is a content-only change with no visual impact and no generated files.

Disclosure

I am affiliated with SandBase AI. This is a free, open-source, source-backed skill submission with no paid placement, affiliate link, or referral incentive. AI assistance was used to draft and validate the listing; the linked source files and behavior were reviewed directly.