docs: explain the P2P diagnostic workflow

Guide users through Diagnostic summary, Diag logging, transfer progress,
symptom checks, and evidence collection from both devices. Link the guide
from the P2P, troubleshooting, reporting, and documentation entry points.
Keep transport compatibility and observation limits explicit.

Validated with the troubleshooting documentation Inspector, 145 local
references, 34 heading anchors, and current English UI labels. Runtime
source and translations are unchanged.

docs/tips/p2p-sync-tips.md

@@ -67,6 +67,8 @@ Keep Obsidian visible and the device awake during initial transfer, rebuild, or
 
 ## Collect evidence
 
+Use the [P2P diagnostic guide](p2p-diagnostics.md) to capture the latest observations, enable **Diag**, and compare transfer progress and logs on both devices before changing settings.
+
 If the same room works on one network but not another, include both network types in the report. Run `Generate full report for opening the issue with debug info`, remove credentials and private relay details, and state whether:
 
 - both devices reached `Connected`;