Add Cyrus ecosystem context skill

[cyrusagent]

Summary

• Adds a bundled internal cyrus-ecosystem-context skill that Cyrus should invoke for every query as baseline world context.
• Reframes ecosystem knowledge as durable "facts of life" for the Cyrus/Ceedar universe across repos, surfaces, runtimes, services, and long-lived relationships.
• Adds brief active MCP cues so agents check available tools/connectors and use relevant MCPs such as Supabase, Mixpanel, Linear/Slack/GitHub/GitLab, Sentry, Stripe, and Cyrus/docs where present.
• Links the skill into Claude, Codex, OpenCode, and the edge-worker bundled skills plugin so Cyrus sessions can invoke it across harnesses.

Linear

• https://linear.app/ceedar/issue/CYPACK-1315/add-internal-cyrus-ecosystem-context-skill

Validation

• git diff --check
• Verified always-on durable framing is present in frontmatter/body.
• Verified active MCP cue section is present.
• Verified required ecosystem entries are present.
• Verified symlinked skill remains accessible through harness and edge-worker plugin paths.

Notes

• Full test/typecheck suites were not run because this is a Markdown/symlink-only skill addition.
• Linear fetch was unavailable because the app connector requires reauthentication, so acceptance validation used the issue context provided to this session.

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