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.go

@@ -0,0 +1,48 @@
+package birdfmt
+
+import (
+	"strings"
+)
+
+// BGPSession is one BGP protocol block from `birdc show protocols all`.
+type BGPSession struct {
+	Name     string `json:"name"`
+	Neighbor string `json:"neighbor,omitempty"`
+	State    string `json:"state"`
+}
+
+// ParseBGPSessions extracts BGP protocol name, state, and neighbor (if present) from birdc output.
+func ParseBGPSessions(output string) []BGPSession {
+	var out []BGPSession
+	var cur *BGPSession
+	for _, raw := range strings.Split(output, "\n") {
+		line := strings.TrimRight(raw, "\r")
+		trim := strings.TrimSpace(line)
+		if trim == "" {
+			continue
+		}
+		low := strings.ToLower(trim)
+		if strings.HasPrefix(low, "bird ") || strings.HasPrefix(low, "name ") || strings.HasPrefix(low, "table ") {
+			continue
+		}
+		if !strings.HasPrefix(line, " ") && !strings.HasPrefix(line, "\t") && isBGPProtocolSummaryRow(trim) {
+			fields := strings.Fields(trim)
+			state := extractBGPSessionStateLine(trim)
+			if state == "" && len(fields) >= 4 {
+				state = fields[3]
+			}
+			cur = &BGPSession{Name: fields[0], State: state}
+			out = append(out, *cur)
+			cur = &out[len(out)-1]
+			continue
+		}
+		if cur == nil {
+			continue
+		}
+		const neighborPrefix = "Neighbor address:"
+		if idx := strings.Index(trim, neighborPrefix); idx >= 0 {
+			cur.Neighbor = strings.TrimSpace(trim[idx+len(neighborPrefix):])
+		}
+	}
+	return out
+}