Added a connection status element that shows current link usage and packet loss.

docs/link_panel.md

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+# Link panel
+
+Run `scenes/link_demo.tscn` with F6. The controls preview connected, near-capacity, saturated, degraded, disconnected, stale and missing telemetry, plus both themes.
+
+```gdscript
+$LinkPanel.set_telemetry(6.42, 1.08, 0.02, 0)
+# down/up: Gbps; packet loss: percent; state: 0 connected, 1 degraded, 2 disconnected
+```
+
+Capacity defaults to 10 Gbps per direction. Arc and direction colors change at 80% and 95%; these thresholds and capacities are configurable. Numeric readings stay in the normal text color and remain unclamped above capacity. Utilization does not change the reported connection state.
+
+`loss_window_seconds` describes the supplied loss measurement (default 10 s); compute that measurement upstream. Disconnected and missing telemetry show dashes. After `stale_after_seconds` (default 2), values are held with a STALE label. Invalid or non-finite samples are rejected. `clear_telemetry()` restores the missing-data state.
+
+Layout and text are scene nodes; `link_rate.gd` only draws the utilization arcs. `link_icon` selects the subdued SVG watermark. The current local chain-link drawing is a draft. Colors come from the shared theme.
+
+The panel replaces the Link placeholder in both layouts and the element library. Existing JSON layouts keep their `link` type IDs. Camera and telemetry transports are not connected by this prototype.