fix(ui): keep a channel row's facepile clear of its pin

[iamnbutler]

Fixes #407

A channel row's facepile was absolutely positioned at the same spot as the row's hover actions. Since #396 the actions take presses without waiting for hover, so pointing at or clicking an avatar hit the invisible pin. On hover the facepile also faded out under the visible pin, which is why its names tooltip never showed on rows (#406).

The facepile and actions now share one trailing cluster at the row's right edge: facepile first, then the actions. Nothing moves on hover, and the pin stays at the right edge where rows without presence show it. The 8px gap equals how far the pin's 40px hit area spills around its 24px button, so the hit area stops at the facepile, and the facepile stacks above it anyway. #396's behavior is unchanged: actions still take a press with no prior hover, and the enlarged hit area still waits for the row's hover. Rows with presence reserve 96px instead of 68px for the cluster, so their titles truncate a little sooner.

Smoke test: a source host (ACE_HOME under /tmp, Tailscale stubbed to exit 1, ACE_DIRECTORY pointed at a local wrangler dev of services/directory) serving this build, plus four scripted teammates in the project's lobby. The host isn't --loopback, because loopback hosts skip lobby subscriptions and would get no presence. In headless Chromium and WebKit, on a row with three people:

• Hovering the leftmost and rightmost avatar hit-tests to the avatar, and the names tooltip shows.
• Clicking either avatar pins nothing.
• Clicking the pin pins, and unpin works.
• In Chromium, a CDP press and release on the pin with no prior mousemove still pins (fix(ui): let a sidebar row's pin button catch the first press #396).

Built in Ace

No — built with Claude Code outside Ace by an overnight issue watcher, because this Mac's Ace Canary is a participant in the running two-person study (#218); dogfooding gap tracked in #5.