Stop the relay checkbox promising a connection this client cannot make

Ticking "Connect through the server relay" moved the host's address and port out of the encrypted payload
into plaintext columns on the server — the single deliberate privacy concession in the design, per ADR 0004
— and then the client dialled the address directly, exactly as it does with the box clear. VaultViewModel
builds SshConnectionRequest(hostname, port, username, credential) and nothing on this side reads
RelayEnabled at all. The connection failed the way it always had, for a machine the laptop could not reach,
with nothing saying the box had done nothing.

The server half is built and shipped: tickets, the WebSocket, the deny list, the CHECK constraint that
enforces a non-null address for a relay-enabled host. What does not exist is the client's path to it, so
this is an unfinished feature rather than a broken one — but the control in front of it was collecting the
cost of the finished version.

Both heads now say so, in the label and in the first sentence of the paragraph under it. Not disabled, and
that is the one decision here worth stating: a host somebody has already ticked has to be able to lose the
flag, and a control greyed out with the concession switched on would trap it there. Tickable and honest
beats untickable and stuck.

This is step 0 of docs/reaching-a-host-you-cannot-dial.md, and the only step of it that should ship alone —
the sentence is written to be deleted when the bridge lands.

VERIFIED. Build clean, 112 layout tests. The drawer's paragraph is longer than it was and the host editor is
measured with the drawer open at the window's minimum, so the wrap is held inside the column rather than
assumed to fit.

src/DodoSSH.Client.App/Views/HostDrawer.axaml

@@ -514,14 +514,25 @@
                 </ComboBox>
 
                 <CheckBox IsChecked="{Binding EditorRelayEnabled}"
-                          Content="Connect through the server relay" />
+                          Content="Connect through the server relay (not wired up yet)" />
                 <!--
                   Stated at the moment the decision is made, which is the only place it means anything. With
                   relay off the server stores no address at all; with it on the server must be able to
                   resolve the target, or it becomes an authenticated open proxy into the operator's network.
+
+                  ◆ AND IT SAYS, FIRST, THAT TICKING IT BUYS NOTHING TODAY. The server half of the relay is
+                  built and this client has no path to it: VaultViewModel dials the address directly whether
+                  this is ticked or not. So the box as it stood spent the one deliberate privacy concession
+                  in the design — the address in plaintext columns — and delivered a connection that failed
+                  exactly as it had before, with nothing saying why.
+
+                  Left tickable rather than disabled, because a host that already carries the flag has to be
+                  able to lose it, and a disabled control would trap the concession on. See
+                  docs/reaching-a-host-you-cannot-dial.md, which is the plan that makes this sentence
+                  removable.
                 -->
                 <TextBlock Classes="hint" FontSize="11"
-                           Text="The relay stores this host's address on the server in plain text. Everything else stays encrypted." />
+                           Text="Not built yet: this client always dials the host itself, so ticking this stores the address on the server and changes nothing about how the host is reached. When it does work, the relay will dial on your behalf — which is why the address and port have to be stored in plain text. Everything else about the host stays encrypted either way." />
 
                 <!--
                   Withdrawing host key trust lives here, in the host's own settings, because a changed host