fix: sync feedback media to Linear

[apronkin]

Published feedback can miss outbound integration delivery, and media embedded in a post is currently stripped before a Linear issue is created. Existing linked issues also cannot be refreshed after their content changes.

This restores post-created event dispatch, adds an admin-only sync action, and preserves images and videos in Linear issue descriptions using absolute URLs. When a post already has an active Linear link, the sync action updates that issue in place; otherwise it queues the normal create flow. The authorization matrix is regenerated for the new server function.

Validation:

• Linear hook, message, and event-dispatch tests: 20 tests passed
• authorization policy suite: 50 tests passed; snapshot regenerated
• oxlint passed (existing repository warnings only)
• git diff --check passed

[CLAassistant]

All committers have signed the CLA.