Worktrees Slots tab: UX fixes seen while photographing prod

Seen on prod's Automation > Slots tab during the docs-writer run (task 7943), as the TimeSaver member: 1. Slots shown as **Destroying** stay in the list with no progress or age. Show how long the removal has been running, and offer a retry or a "dismiss" once it is clearly stuck. 2. The row's Git column renders a run of glyphs ("— ? ? —") with no column header. Give the list column headers (Git, Stack, Session, Age), or put the meaning in a visible label instead of only in a tooltip. 3. When the plan includes no static slots, the toolbar shows a greyed **Add slots** and the list shows a banner saying the same thing. Keep one: either hide the button and keep the banner, or keep the button with its tooltip and drop the banner. 4. A main clone's details drawer leaves a large empty area below **Delete slot**. Pin the actions to the bottom, or let the drawer size to its content. 5. Node names render as raw ids (for example "shared-0bf8d8d7"). Show the node's display name, and keep the id as secondary text. Out of scope: slot lifecycle and erase behaviour on nodes; plan entitlements. Done means: each item is either fixed and visible on the Slots tab at desktop and phone widths, or answered with the reason it stays as is; the web tests for WorktreePool pass.

Slots tab: destroy age + Stuck/Dismiss, column headers, no-static Add hidden (banner kept), drawer Release/Delete pinned; node-name item answered (it is the real generated name, draft #7981). Quick gate + tests green, visual checked; PR #6235 queued.