feat(shard)!: declare wire protocol 3

The site's declared version is the admin-set uo_link_config.protocol column, so
the sidecar's PROTOCOL_VERSION 2 -> 3 bump has to be matched here or every REST
call 409s and uoLinkSocket closes the WS on the ws.hello mismatch. Five places
carry the number and all five move together: the column default, the model's
DEFAULT_PROTOCOL (what a site with nothing saved yet declares), the two
`config.protocol || 1` fallbacks in uoLinkClient/uoLinkSocket -- unreachable
today, but an unset value quietly sending 1 is exactly the confusing 409 the
version check exists to prevent -- the admin form's initial value, and the
documented env default.

The boot migration is the only subtle part. schema.sql is re-run on EVERY boot,
and `protocol` is admin-editable, so a bare UPDATE would silently un-pin an
operator who had deliberately pinned an older sidecar in Admin -> Shard. It is
therefore gated on a marker row in `settings`, written after the UPDATE: the
first boot on this build migrates, every later boot is a no-op. `protocol < 3`
rather than `= 2` picks up an install still on the old default of 1, which could
not have been talking to a v2 sidecar anyway. A fresh install has no row to
update and just gets the marker plus the new column default.

Verified against the local MariaDB through ensureSchema (the production path):
2 -> 3 with the marker written and the column default now 3; pinned back to 2 by
hand, re-ran, and it STAYED 2 -- the one-shot property holds. 673 server tests,
47 client tests, client build green.

Co-Authored-By: Claude <noreply@anthropic.com>

client/src/routes/admin/views/ShardAdmin.jsx

@@ -155,7 +155,7 @@ export default function ShardAdmin() {
   const [baseUrl, setBaseUrl] = useState('')
   const [wsUrl, setWsUrl] = useState('')
   const [token, setToken] = useState('')
-  const [protocol, setProtocol] = useState(1)
+  const [protocol, setProtocol] = useState(3)
   const [enabled, setEnabled] = useState(false)
   const [busy, setBusy] = useState(false)
   const [msg, setMsg] = useState('')
@@ -172,7 +172,7 @@ export default function ShardAdmin() {
       if (!initializedRef.current) {
         setBaseUrl(c.baseUrl || '')
         setWsUrl(c.wsUrl || '')
-        setProtocol(c.protocol || 1)
+        setProtocol(c.protocol || 3)
         setEnabled(c.enabled)
         initializedRef.current = true
       }