docs: add Gitea milestone tracking instructions to all phase docs

Each phase doc now includes:
- Milestone Tracking section linking to the corresponding Gitea milestone
- Checklist item in Completion Criteria to close the milestone
- Phase 7 also closes the Final: Porting Complete milestone (ID 8)

docs/plans/phases/phase-4-dotnet-design.md

@@ -16,6 +16,10 @@ Every module, feature, and test in the porting database must have either a .NET
 - **Go source code** is located in the `golang/` folder (specifically `golang/nats-server/`)
 - **.NET ported version** is located in the `dotnet/` folder
 
+## Milestone Tracking
+
+This phase corresponds to **Milestone 4** in [Gitea](https://gitea.dohertylan.com/dohertj2/natsnet/milestone/4). When starting this phase, verify the milestone is open. Assign relevant issues to this milestone as work progresses.
+
 ## Solution Structure
 
 Define the .NET solution layout following standard conventions:
@@ -185,6 +189,14 @@ dotnet run --project tools/NatsNet.PortTracker -- feature list --status n_a --db
 - Every test has `dotnet_project`, `dotnet_class`, and `dotnet_method` set, or status is `n_a` with a reason
 - Naming follows PascalCase and the namespace hierarchy described above
 - No two features map to the same class + method combination (collisions)
+- [ ] Close the Phase 4 milestone in Gitea:
+  ```bash
+  curl -s -X PATCH "https://gitea.dohertylan.com/api/v1/repos/dohertj2/natsnet/milestones/4" \
+    -H "Content-Type: application/json" \
+    -H "Authorization: token $GITEA_TOKEN" \
+    -d '{"state":"closed"}'
+  ```
+  Or close it via the Gitea web UI at https://gitea.dohertylan.com/dohertj2/natsnet/milestone/4
 
 ## Related Documentation