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/pages/sessions.tsx

@@ -266,7 +266,7 @@ export const SessionsPage = () => {
               <h2>Last Session</h2>
               <div className="card last-session-card">
                 <div className="last-session-info">
-                  <h3>{lastSession.display_name}</h3>
+                  <h3>{lastSession.display_name || lastSession.tool_type_name || "Unnamed Session"}</h3>
                   <p className="muted">
                     {lastSession.tool_type_name} · {lastSession.project_name} · {lastSession.repository_name}
                   </p>
@@ -316,7 +316,7 @@ export const SessionsPage = () => {
                 {activeSessions.map((session) => (
                   <div className="card session-card" key={session.id}>
                     <div className="session-info">
-                      <h4>{session.display_name}</h4>
+                      <h4>{session.display_name || session.tool_type_name || "Unnamed Session"}</h4>
                       <p className="muted">
                         {session.tool_type_name} · {session.project_name}
                       </p>
@@ -445,7 +445,7 @@ export const SessionsPage = () => {
                 {recentSessions.map((session) => (
                   <div className="recent-session-item" key={session.id}>
                     <div className="recent-session-info">
-                      <span className="recent-session-name">{session.display_name}</span>
+                      <span className="recent-session-name">{session.display_name || session.tool_type_name || "Unnamed Session"}</span>
                       <span className="muted">
                         {session.tool_type_name} · {session.project_name}
                       </span>