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.

public/style.css

@@ -659,3 +659,144 @@ body {
   background: var(--red);
   color: #2a0808;
 }
+
+/* ── Session Manager page (manage.html) ──────────────────────────── */
+#manage-root {
+  max-width: 760px;
+  margin: 0 auto;
+  padding: 24px 16px 60px;
+}
+.mg-header {
+  margin-bottom: 18px;
+}
+.mg-title {
+  font-size: 22px;
+  font-weight: 700;
+  color: #fff;
+}
+.mg-sub {
+  color: var(--text-dim);
+  font-size: 13px;
+  margin-top: 2px;
+}
+.mg-bar {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 8px;
+  margin-top: 14px;
+}
+.mg-btn {
+  background: var(--surface-2);
+  border: 1px solid var(--border-strong);
+  color: var(--text);
+  border-radius: 8px;
+  padding: 8px 14px;
+  cursor: pointer;
+  font: inherit;
+  font-size: 13px;
+  text-decoration: none;
+  transition: background 0.1s ease;
+}
+.mg-btn:hover {
+  background: var(--surface-3);
+}
+.mg-btn.warn {
+  border-color: rgba(245, 177, 76, 0.5);
+  color: var(--amber);
+}
+.mg-btn.danger {
+  border-color: rgba(255, 107, 107, 0.5);
+  color: var(--red);
+}
+.mg-list {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+}
+.mg-row {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  padding: 12px 14px;
+  background: var(--surface-2);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+}
+.mg-main {
+  flex: 1 1 auto;
+  min-width: 0;
+}
+.mg-top {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+.mg-name {
+  color: #fff;
+  font-weight: 600;
+}
+.mg-watch {
+  font-size: 11px;
+  color: var(--text-faint);
+  background: var(--surface-3);
+  border-radius: 5px;
+  padding: 1px 6px;
+}
+.mg-watch.live {
+  color: var(--green);
+  background: rgba(70, 208, 127, 0.14);
+}
+.mg-status {
+  font-size: 11px;
+  color: var(--text-dim);
+}
+.mg-status.mg-waiting {
+  color: var(--amber);
+  font-weight: 600;
+}
+.mg-status.mg-working {
+  color: var(--accent);
+}
+.mg-meta {
+  color: var(--text-faint);
+  font-size: 12px;
+  margin-top: 3px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  font-family: Menlo, Consolas, monospace;
+}
+.mg-actions {
+  flex: none;
+  display: flex;
+  gap: 6px;
+}
+.mg-open {
+  background: var(--accent);
+  color: #fff;
+  border-radius: 8px;
+  padding: 7px 13px;
+  text-decoration: none;
+  font-size: 13px;
+}
+.mg-open:hover {
+  background: var(--accent-2);
+}
+.mg-kill {
+  background: transparent;
+  border: 1px solid rgba(255, 107, 107, 0.4);
+  color: var(--red);
+  border-radius: 8px;
+  padding: 7px 13px;
+  cursor: pointer;
+  font: inherit;
+  font-size: 13px;
+}
+.mg-kill:hover {
+  background: rgba(255, 107, 107, 0.14);
+}
+.mg-empty {
+  color: var(--text-dim);
+  padding: 30px 0;
+  text-align: center;
+}