fix: terminal shift-left bug and session sidebar naming/filtering

- Guard ResizeObserver in terminal against internal xterm DOM changes
  by tracking last width/height and only calling fit() on real resize
- Remove padding from .terminal-container and conflicting .xterm height
  override that caused measurement mismatches with xterm-addon-fit
- Filter live session sidebar to active statuses only (running, building,
  pending) instead of showing all sessions including stopped ones
- Add display name fallback across sidebar, sessions page, and instance
  list to prevent blank names when display_name is empty

Quality gates: tsc (pass), eslint (pass)

apps/web/src/components/instance-list.tsx

@@ -194,7 +194,7 @@ export const InstanceList = ({ projectId, repoId, toolTypes }: InstanceListProps
           {instances.map((instance) => (
             <div key={instance.id} className="instance-card">
               <div className="instance-info">
-                <div className="instance-name">{instance.display_name}</div>
+                <div className="instance-name">{instance.display_name || instance.tool_type_name || "Unnamed Instance"}</div>
                 <div className="instance-meta">
                   <span
                     className="status-dot"