Aggiunto connector Context7 (mcp_remote)

- URL: https://mcp.context7.com/mcp, trasporto streamable-http
- Auth: none (endpoint pubblico, free tier)
- Verify: MCP initialize probe (testato ✅)
- Icone SVG dal logo ufficiale Context7

Inoltre:
- Copiata docs/connector.manifest_guide.md da skald-circle/blueprint/
- Riferimento alla guida in SKALD.md

connectors/context7/icon_sm.svg

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