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)

.gitignore

@@ -48,3 +48,8 @@ apps/web/dist/
 # OS
 .DS_Store
 Thumbs.db
+
+# Local runtime state
+.atl/
+.pi/
+swap-pane