fix(v0.4): mirror size-clamp bug + session manager page

The mirror looked broken because a backgrounded tab on one device still pinned
the shared PTY to its (default 80x24) size — so the device actively viewing got
a cramped terminal.

Fix: only an ACTIVELY-VIEWING client votes on PTY size.
- attachWs no longer seeds a default size vote (a join may be a hidden mirror)
- new 'blur' client message + clearClientDims(): a tab going hidden withdraws its
  size vote (still mirrors output); show() re-casts it
- PTY size = min cols/rows across clients that have actually reported dims
- session/protocol tests cover hidden-mirror-doesn't-clamp + blur

Session manager (separate page, for the 'too many sessions' problem):
- GET stays; add DELETE /live-sessions/:id and DELETE /live-sessions[?detached=1]
- manager.killById(); LiveSessionInfo gains cols/rows
- public/manage.html + manage.ts: list/open/kill sessions, kill-all / kill-detached,
  auto-refresh; 🗂 toolbar button; bundled as a 2nd esbuild entry

Verified: two concurrent clients mirror output + shared input; manage page
lists/kills (3→2→0). 225 tests green, tsc clean.

src/types.ts

@@ -45,6 +45,9 @@ export type ClientMessage =
   | { type: 'attach'; sessionId: string | null; cwd?: string }
   | { type: 'input'; data: string }
   | { type: 'resize'; cols: number; rows: number }
+  // v0.4: this client stopped actively viewing (tab hidden) — withdraw its size
+  // vote so a background mirror doesn't clamp the shared PTY (min-dims).
+  | { type: 'blur' }
   | { type: 'approve' }
   | { type: 'reject' };
 
@@ -167,10 +170,11 @@ export interface Session {
 // impl anchors [src/session/session.ts]:
 //   createSession(cfg: Config, dims: Dims, now: number, onExit: (s: Session) => void): Session
 //                                                  // spawn failure THROWS, not swallowed (M4)
-//   attachWs(session: Session, ws: WebSocketLike, dims: Dims): void  // adds a client, replays buffer (no kick)
+//   attachWs(session: Session, ws: WebSocketLike): void             // adds a client, replays buffer (no size vote until it resizes)
 //   detachWs(session: Session, ws: WebSocketLike, now: number): void // removes one client; never kills PTY
 //   writeInput(session: Session, data: string): void                // no-op after exit (L4)
-//   setClientDims(session: Session, ws: WebSocketLike, cols, rows): void  // PTY = min over clients (L4 no-op after exit)
+//   setClientDims(session: Session, ws: WebSocketLike, cols, rows): void  // PTY = min over active viewers (L4 no-op after exit)
+//   clearClientDims(session: Session, ws: WebSocketLike): void      // withdraw this client's size vote (tab hidden / blur)
 //   kill(session: Session): void
 
 /* ──────────────────────── manager (§3.5) ─────────────────────── */
@@ -183,6 +187,8 @@ export interface LiveSessionInfo {
   status: ClaudeStatus;
   exited: boolean;
   cwd: string | null;
+  cols: number; // current PTY size (for the manage page)
+  rows: number;
 }
 
 export interface SessionManager {
@@ -196,6 +202,9 @@ export interface SessionManager {
   get(id: string): Session | undefined;
   /** Live sessions for multi-device discovery (newest first). */
   list(): LiveSessionInfo[];
+  /** Kill a session by id (manage page): close its clients, kill the PTY, drop it.
+   *  Returns true if a session was found and killed. */
+  killById(id: string): boolean;
   /** Set a session's Claude status (from a hook) and push it to the attached ws (H2/H3). */
   handleHookEvent(
     sessionId: string,