Add generic agent-session webhook trigger

[cyrusagent]

Assignee: @PaytonWebber (payton)

Summary

• Adds a first-class POST /agent-session-webhook endpoint for trusted generic surfaces, authenticated with CYRUS_API_KEY.
• Defines a versioned generic webhook contract with stable session binding, prompt/resume/stop events, callback support, and idempotency handling.
• Replaces the Slack-only ChatSessionHandler with AgentSessionLifecycleService, so Slack and generic surface sessions share one create/resume/inject/reply lifecycle backed by the primary AgentSessionManager.
• Adds generic allowed-tool and MCP config settings, regenerates config JSON schemas, and updates exports/tests/F1 docs.

Validation

• pnpm typecheck
• pnpm lint (passes with existing warnings)
• pnpm test:packages:run
• pnpm build
• F1 test drive: apps/f1/test-drives/2026-06-09-cypack-1300-generic-agent-session-webhook.md

Linear: https://linear.app/ceedar/issue/CYPACK-1300/add-generic-agent-session-webhook-trigger-copy

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