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-1-decomposition.md

@@ -33,6 +33,10 @@ echo $CGO_ENABLED   # should print 1 (or be unset; we set it explicitly below)
 | Go source code | `golang/` (specifically `golang/nats-server/`) |
 | .NET ported version | `dotnet/` |
 
+## Milestone Tracking
+
+This phase corresponds to **Milestone 1** in [Gitea](https://gitea.dohertylan.com/dohertj2/natsnet/milestone/1). When starting this phase, verify the milestone is open. Assign relevant issues to this milestone as work progresses.
+
 ## Steps
 
 ### Step 1: Initialize the porting database
@@ -230,6 +234,15 @@ Phase 1 Checklist:
 Note: The "All libraries mapped" item will be unchecked -- that is expected.
 Library mapping is the concern of Phase 3.
 
+- [ ] Close the Phase 1 milestone in Gitea:
+  ```bash
+  curl -s -X PATCH "https://gitea.dohertylan.com/api/v1/repos/dohertj2/natsnet/milestones/1" \
+    -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/1
+
 ## Troubleshooting
 
 ### CGO_ENABLED not set or build fails with "gcc not found"