feat(v0.6): kill a session directly from the Projects grid cards

The detail view could kill sessions, but the grid card's session rows were
enter-only. Add a ✕ kill button to each card session row (stopPropagation so it
doesn't also enter the session); makeSessionRow gains an optional onKill,
makeProjectCard an optional onKillSession, and mountProjects wires it to
DELETE /live-sessions/:id followed by a refresh.

Frontend-only. projects-panel tests +1 (51): ✕ present only with the callback,
click kills the right id without entering. Verified in-browser: a card with 2
sessions dropped to 1 after clicking ✕.

test/projects-panel.test.ts

@@ -324,6 +324,25 @@ describe('makeProjectCard — launcher row', () => {
     expect(card.querySelectorAll('.proj-launch')).toHaveLength(3)
   })
 
+  it('shows a Kill (✕) on each session row only when onKillSession is given', () => {
+    const p = makeProject({
+      sessions: [{ id: 's1', status: 'idle', clientCount: 1, createdAt: 1, exited: false }],
+    })
+    // Without the callback: no kill button (enter-only).
+    const plain = makeProjectCard(p, new Set(), noopHooks(), () => {})
+    expect(plain.querySelector('.proj-session-kill')).toBeNull()
+
+    // With the callback: clicking ✕ kills that session and does not enter it.
+    const hooks = noopHooks()
+    const onKill = vi.fn()
+    const card = makeProjectCard(p, new Set(), hooks, () => {}, undefined, onKill)
+    const kill = card.querySelector('.proj-session-kill') as HTMLButtonElement
+    expect(kill).not.toBeNull()
+    kill.click()
+    expect(onKill).toHaveBeenCalledWith('s1')
+    expect(hooks.onEnterSession).not.toHaveBeenCalled()
+  })
+
   it('highlights the Claude launcher when a Claude session (known status) is live', () => {
     const p = makeProject({
       sessions: [{ id: 's1', status: 'working', clientCount: 0, createdAt: 1, exited: false }],