feat(profiles): open targeted agent editor from owner profile

[kalvinnchau]

Summary

• Add an owner-gated “Agent instructions” entry in the profile pane using the existing edit interface and matching base Buzz copy.
• Register a versioned Agents-page edit route that selects one exact native identity in the active community.
• Cover owner visibility, selected-agent targeting, route lifecycle, and failure/retry behavior.

Verification

• Full Vitest suite: 342 files, 3,709 tests passed.
• Typecheck, lint, staged formatting, design-system checks, related pre-push tests, and diff check passed.
• Rendered Chromium and WebKit validation exercised owner ingress, exact targeting, save/retry, connecting readiness, close/Back, and stale-target card editing.