fix(guilds): do not offer linking where linking cannot reach

Found on the live rig, with the shard's guild feature gated to staff: the
refusal still read "link your account — this shard shows guild information to
linked players". Signing in reaches `logged_in` and linking a game account
reaches `player`; `staff` and `admin` are roles an operator grants, and no
amount of linking earns them. Inviting someone to do something that changes
nothing is worse than plainly saying no.

Also drops the host name from the list embed's title. `ctx.site` carries a base
URL and no brand name, so naming the deployment there could only ever mean
printing its hostname into a title on the shard's own Discord server.

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

server/test/guildCommand.test.js

@@ -88,6 +88,14 @@ test('an unlinked caller is invited to link — but only when linking would chan
   stub({ audience: 'anonymous', level: 'anonymous' })
   const open = await command.handler({ options: {}, actor: anonymous })
   assert.equal(open.notice, null)
+
+  // Gated to staff: linking reaches `player` and stops there, so the invitation
+  // would be an instruction to do something that changes nothing. Found on the
+  // live rig, where a staff-gated shard still offered it.
+  stub({ audience: 'staff', level: 'anonymous' })
+  const unreachable = await command.handler({ options: {}, actor: anonymous })
+  assert.match(unreachable.text, /not shown to your account/)
+  assert.equal(unreachable.notice, null)
 })
 
 test('a stale board answers offline rather than reporting what it still holds', async () => {
@@ -99,6 +107,7 @@ test('a stale board answers offline rather than reporting what it still holds',
 test('no argument lists the largest guilds', async () => {
   stub()
   const res = await command.handler({ options: {}, actor: anonymous })
+  assert.equal(res.title, 'Guilds on this shard')
   assert.equal(res.fields.length, 2)
   assert.match(res.fields[0].name, /Knights of the Codex/)
   assert.match(res.fields[0].value, /12 members · 3 online/)