docs: mark M3 Local DNS Listener as done

DEVELOP.md

@@ -87,7 +87,7 @@ See [docs/plan.md](docs/plan.md) for the full project plan and milestone checkli
 |-----------|--------|
 | M1 — Core Forwarding | ✅ Done |
 | M2 — Multiple Upstreams & Config | ✅ Done |
-| M3 — Local DNS Listener | 🔲 Not started |
+| M3 — Local DNS Listener | ✅ Done |
 | M4 — Caching | 🔲 Not started |
 | M5 — Observability | 🔲 Not started |
 | M6 — Blocking & Filtering | 🔲 Not started |

docs/plan.md

@@ -58,12 +58,12 @@ A lightweight DNS-over-HTTPS (DoH) forwarder that accepts DNS queries over HTTPS
 
 ### M3 — Local DNS Listener
 
-- [ ] UDP listener on configurable port (default 53)
-- [ ] TCP listener on configurable port (default 53)
-- [ ] Receive standard DNS wire-format queries
-- [ ] Forward through DoH pipeline (shared upstream client)
-- [ ] Return DNS wire-format response over UDP/TCP
-- [ ] Config: `[dns]` section with `listen` address
+- [x] UDP listener on configurable port (default 53)
+- [x] TCP listener on configurable port (default 53)
+- [x] Receive standard DNS wire-format queries
+- [x] Forward through DoH pipeline (shared upstream client)
+- [x] Return DNS wire-format response over UDP/TCP
+- [x] Config: `[dns]` section with `listen` address
 - [ ] Integration test with UDP/TCP clients
 
 ### M4 — Caching