feat(api): enhance peer session management and documentation

- Added new fields to the API for tracking connected speakers and session states across multiple nodes, including `connected_speaker_id`, `connected_speaker_label`, `session_on_speakers`, `established_on_speakers`, and `session_mismatch`.
- Implemented a new endpoint for retrieving bird protocol sessions, enhancing the agent server functionality.
- Updated the OpenAPI documentation to reflect the new fields and query parameters, improving clarity for API consumers.
- Modified the frontend to display connected speaker information and session states, providing better visibility into peer connections.
- Updated deployment documentation to clarify the configuration requirements for enabling IP forwarding on VPS.

internal/birdfmt/bgp_sessions_test.go

@@ -0,0 +1,26 @@
+package birdfmt
+
+import "testing"
+
+func TestParseBGPSessions_neighborAndState(t *testing.T) {
+	sample := `
+BIRD 2.14 ready.
+Name       Proto      Table      State  Since         Info
+device1    Device     ---        up     10:00:00
+evobgp_p_abc123 BGP      master4    up     10:00:05     Established
+  Neighbor address: 198.51.100.2
+  Neighbor AS:    65001
+evobgp_p_def456 BGP      master4    up     10:00:06     Active
+  Neighbor address: 2001:db8::2
+`
+	sessions := ParseBGPSessions(sample)
+	if len(sessions) != 2 {
+		t.Fatalf("got %d sessions want 2", len(sessions))
+	}
+	if sessions[0].Name != "evobgp_p_abc123" || sessions[0].State != "Established" || sessions[0].Neighbor != "198.51.100.2" {
+		t.Fatalf("session0: %+v", sessions[0])
+	}
+	if sessions[1].Neighbor != "2001:db8::2" || sessions[1].State != "Active" {
+		t.Fatalf("session1: %+v", sessions[1])
+	}
+}