feat(v0.6): remove standalone Manage page — manage sessions on the Sessions view

The Sessions chooser already shows every running session with a live thumbnail
and Open + New session, so fold delete into it and drop the separate page:

- add a Kill ✕ button to each session card (DELETE /live-sessions/:id + refresh),
  reusing makePreviewCard's extraActions and the existing .mg-kill style
- remove public/manage.html + public/manage.ts and the esbuild manage entry
- remove the 🗂 toolbar button (main.ts) and the 🗂 Manage header link (launcher.ts)

Backend DELETE/preview routes stay (used by the launcher kill, thumbnails, and
the project pages). Frontend + build-config only.

Verified: full suite 453 green, web typecheck clean, build:web emits only main
(no manage.* artifacts), and in-browser the Sessions cards have Open + Kill (2→1
on kill), no Manage entry, and GET /manage.html → 404.

public/launcher.ts

@@ -45,9 +45,7 @@ export function mountLauncher(host: HTMLElement, hooks: LauncherHooks): Launcher
   const actions = el('div', 'launcher-actions')
   const newBtn = el('button', 'launcher-new', '＋ New session')
   newBtn.addEventListener('click', () => hooks.onNew())
-  const manage = el('a', 'mg-btn', '🗂 Manage') as HTMLAnchorElement
-  manage.href = '/manage.html'
-  actions.append(newBtn, manage)
+  actions.append(newBtn)
   head.append(sub, actions)
   root.append(head)
 
@@ -57,8 +55,20 @@ export function mountLauncher(host: HTMLElement, hooks: LauncherHooks): Launcher
   const cards = new Map<string, PreviewCard>()
   let timer: ReturnType<typeof setInterval> | null = null
 
+  /** Kill a session (DELETE /live-sessions/:id) then refresh the grid. */
+  async function killOne(id: string): Promise<void> {
+    await fetch(`/live-sessions/${encodeURIComponent(id)}`, { method: 'DELETE' }).catch(() => {})
+    void refresh()
+  }
+
   function makeCard(s: LiveSessionInfo): PreviewCard {
-    return makePreviewCard(s, { onOpen: (id) => hooks.onOpen(id) })
+    const kill = el('button', 'mg-kill', 'Kill ✕')
+    kill.title = 'Kill this session'
+    kill.addEventListener('click', () => void killOne(s.id))
+    return makePreviewCard(s, {
+      onOpen: (id) => hooks.onOpen(id),
+      extraActions: () => [kill],
+    })
   }
 
   async function refresh(): Promise<void> {