Add Tailscale connection method monitoring

Add connection_method field to NetworkInterfaceData to track whether
Tailscale is using direct P2P, DERP relay, or HTTP proxy connections.
The connection method is displayed as a sub-service under tailscaled
service, following the same pattern as VPN routes and firewall ports.

Query tailscale status --json to determine active connection type and
display as informational sub-service when tailscaled is active.

Cargo.lock

@@ -279,7 +279,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.259"
+version = "0.1.260"
 dependencies = [
  "anyhow",
  "chrono",
@@ -301,7 +301,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.259"
+version = "0.1.260"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -325,7 +325,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.259"
+version = "0.1.260"
 dependencies = [
  "chrono",
  "serde",