feat(config): default tcp/quic listen ports to mycelium standard 9651/9652

Pinning ephemeral ports made the existing field useful but left the
default behaviour (random port at every start) hostile to the
typical private-network setup, where the user pre-configures a
port-forward on their home router and expects mycelium to keep
using the same port.

Default to 9651 (TCP) and 9652 (QUIC), which match the public
mycelium convention. Clearing either field still falls back to
ephemeral. Help text updated; placeholder now says "leave empty
for ephemeral" instead of "ephemeral" so users understand the
field is currently filled with the default.

src/stores/config.ts

@@ -8,14 +8,16 @@ const KEY = "sidecar";
 
 // A private overlay has no Threefold-operated seed peer. The user must
 // declare bootstrap peers they trust (their own VPS, known friends…)
-// before the daemon can usefully start.
+// before the daemon can usefully start. Default to mycelium's
+// well-known peer-listen ports (9651 TCP, 9652 QUIC) so port-forwards
+// on a home router are predictable from the first run.
 const DEFAULT_CONFIG: SidecarConfig = {
   peers: [],
   tunName: null,
   noTun: false,
   networkName: null,
-  tcpListenPort: null,
+  tcpListenPort: 9651,
-  quicListenPort: null,
+  quicListenPort: 9652,
 };
 
 function normalizePort(p: unknown): number | null {

src/views/Settings.vue

@@ -412,7 +412,7 @@ onMounted(async () => {
               type="text"
               inputmode="numeric"
               class="mt-1 w-full rounded-md border border-input bg-background px-3 py-1.5 font-mono text-sm focus:outline-none focus:ring-2 focus:ring-ring"
-              placeholder="ephemeral"
+              placeholder="leave empty for ephemeral"
             />
           </div>
           <div>
@@ -424,16 +424,15 @@ onMounted(async () => {
               type="text"
               inputmode="numeric"
               class="mt-1 w-full rounded-md border border-input bg-background px-3 py-1.5 font-mono text-sm focus:outline-none focus:ring-2 focus:ring-ring"
-              placeholder="ephemeral"
+              placeholder="leave empty for ephemeral"
             />
           </div>
         </div>
         <p class="text-[11px] text-muted-foreground">
-          Pin these to a fixed value (e.g. <code class="font-mono">9651</code> for
+          Defaults are <code class="font-mono">9651</code> (TCP) and
-          TCP, <code class="font-mono">9652</code> for QUIC) when you port-forward
+          <code class="font-mono">9652</code> (QUIC) — the conventional mycelium
-          a stable port on your router so other private-network nodes can dial in
+          peer-listen ports, predictable for port-forwarding on a home router.
-          across daemon restarts. Leave empty to keep using a different ephemeral
+          Clear the field to fall back to a random ephemeral port at every start.
-          port at every start.
         </p>
         <div class="flex justify-end gap-2 pt-2">
           <button