feat(infra): exponer pane_id (%N) estable en el JSON de la flota

El orquestador identificaba cada agente por el campo tmux_window (@N), pero
el window_id de tmux cambia cuando un pane entra/sale de windows (el focus de
la flota usa break-pane + join-pane, que recrean windows). El pane_id (%N) en
cambio es estable durante toda la vida del pane: es el identificador correcto.

- claude_fleet.go: nuevo campo ClaudeFleet.PaneID `json:"pane_id"`. Se mantiene
  TmuxWindow (lo necesita el focus internamente); esto AÑADE pane_id, no lo
  reemplaza.
- resolve_pane_ids.go (+ .md, .go test): nueva función del registry
  ResolvePaneIDs(socket, pids) -> map[pid]pane_id. Lista los panes del socket
  (tmux -L <socket> list-panes -a) y para cada PID sube por el árbol de procesos
  (PPID en /proc) hasta dar con un pane_pid. Reutiliza runTmux y procPPID del
  paquete infra. Best-effort: tmux/socket caído o PID sin pane -> "" sin crash.
  Núcleo testeable con inyección de la salida tmux y del resolvedor de PPID.
- list_claude_fleet.go: ListClaudeFleet() puebla PaneID resolviendo cada PID
  vivo contra $FLEET_SOCKET (default "fleet"). Solo la entrada pública lo hace;
  ListClaudeFleetFrom() queda intacta (cero coste tmux en tests y en el bucle
  de render de fleetview).

Tag de grupo: orchestration.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

functions/infra/resolve_pane_ids_test.go

@@ -0,0 +1,80 @@
+//go:build !windows && linux
+
+package infra
+
+import (
+	"reflect"
+	"testing"
+)
+
+// fakePPID builds a ppidOf closure from a child->parent map. Unknown PIDs map to
+// 1 (init), which terminates the ascent without matching any pane.
+func fakePPID(tree map[int]int) func(int) int {
+	return func(pid int) int {
+		if p, ok := tree[pid]; ok {
+			return p
+		}
+		return 1
+	}
+}
+
+func TestResolvePaneIDsFrom(t *testing.T) {
+	// Two panes. Pane %3 runs claude directly (pane_pid == claude PID 100).
+	// Pane %7 runs a shell (pane_pid 200) that launched claude as a child (300).
+	tmuxOut := "100 %3\n200 %7\n"
+	tree := map[int]int{
+		300: 200, // claude (300) -> shell (200) which is the pane_pid of %7
+	}
+
+	got := resolvePaneIDsFrom(tmuxOut, fakePPID(tree), []int{100, 300})
+	want := map[int]string{
+		100: "%3", // direct: pane_pid IS the claude PID
+		300: "%7", // ascent: claude's parent is the pane_pid
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("resolvePaneIDsFrom = %v, want %v", got, want)
+	}
+}
+
+func TestResolvePaneIDsFromUnresolvable(t *testing.T) {
+	// PID 999 has no pane in its ancestry -> omitted (caller degrades to "").
+	tmuxOut := "100 %3\n"
+	got := resolvePaneIDsFrom(tmuxOut, fakePPID(map[int]int{}), []int{999})
+	if len(got) != 0 {
+		t.Fatalf("expected empty map for unresolvable PID, got %v", got)
+	}
+}
+
+func TestResolvePaneIDsFromMalformedLines(t *testing.T) {
+	// Garbage / short / non-numeric lines are skipped without crashing; the one
+	// valid line still resolves.
+	tmuxOut := "\n  \nnotapid %9\n42\n100 %3\n"
+	got := resolvePaneIDsFrom(tmuxOut, fakePPID(map[int]int{}), []int{100})
+	want := map[int]string{100: "%3"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("resolvePaneIDsFrom (malformed) = %v, want %v", got, want)
+	}
+}
+
+func TestResolvePaneIDsEmptyInputs(t *testing.T) {
+	// Empty socket or no PIDs -> empty map, no tmux call attempted.
+	if got := ResolvePaneIDs("", []int{1, 2}); len(got) != 0 {
+		t.Errorf("empty socket: expected empty map, got %v", got)
+	}
+	if got := ResolvePaneIDs("fleet", nil); len(got) != 0 {
+		t.Errorf("nil pids: expected empty map, got %v", got)
+	}
+}
+
+func TestPaneAncestorBounded(t *testing.T) {
+	// A cycle in the process tree must not hang: the 64-hop bound cuts it.
+	cycle := func(pid int) int {
+		if pid == 500 {
+			return 501
+		}
+		return 500 // 501 -> 500 -> 501 ... never reaches a pane
+	}
+	if id, ok := paneAncestor(500, map[int]string{100: "%3"}, cycle); ok {
+		t.Fatalf("expected no resolution for cyclic tree, got %q", id)
+	}
+}