Add a subagent roster command

[gantoine]

Problem

PostHog Code already supports bundled and project-local subagents with per-agent model and reasoning overrides, but there is no quick way to inspect the effective roster. A discoverable roster makes the configuration visible before delegating work.

Changes

• Add /subagents to show bundled agents and their effective model, reasoning level, and purpose.
• Add /subagents all to include project-local agents while respecting project trust settings.
• Document the command and cover formatting behavior with focused tests.

How did you test this?

• pnpm --filter @posthog/shared build
• pnpm --filter @posthog/harness typecheck
• pnpm --filter @posthog/harness exec vitest run src/extensions/subagent/roster.test.ts src/extensions/subagent/agents.test.ts src/extensions/subagent/settings.test.ts
• pnpm exec biome check --write packages/harness/src/extensions/subagent/extension.ts packages/harness/src/extensions/subagent/roster.ts packages/harness/src/extensions/subagent/roster.test.ts
• git diff --check

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit b3c9cb5.}