Feat(UI): Add Human page & Replace Delete with DM for pop-up profile

[xxx7xxxx]

Summary

• Adds a first-class Human section in the Agents tab, with /humans/:id routing and a human detail page for the current user.
• Lets users edit their human avatar through the shared avatar picker and syncs participant avatar updates back to the IM user record.
• Replaces the profile preview Delete action with a DM action, including manager previews.

Validation

• Inspected HEAD diff and git show --check --summary HEAD.
• Tests were added/updated for human routing, sidebar placement, profile preview actions, i18n, participant avatar sync, and task room expectations, but I did not rerun the test suites in this turn.