fix(multiplayer): requeue every participant after a proposal times out

The timeout sibling of the previous commit's decline fix: a proposal
that simply times out (the 10s window elapses with no unanimous
response) hits ProposalExpireSQL/ProposalParticipantExpireSQL, and
neither of those -- same as the decline path -- ever touched
queue_tickets. Same severe consequence: every participant still
holding a PROPOSED ticket, response pending or already accepted, is
left stranded (invisible to the matcher, blocking a fresh
queue_create, renewable forever by heartbeat) with no automatic way
back into matchmaking. This path is reached from both GetProposal
(the recovery/read boundary -- a client that missed the expiry event
entirely) and RespondToProposal (a response arriving after the
window), so both needed the fix.

ProposalExpireRequeueSQL mirrors ProposalDeclineRequeueSQL, guarded on
state = 'EXPIRED' so it's safe to call unconditionally right after
ProposalExpireSQL: a no-op on a proposal that's still OPEN, and a
no-op on a proposal that was already EXPIRED on a prior pass (nothing
left at PROPOSED to requeue a second time).

Covered by a real PostgreSQL integration test via GetProposal (nobody
ever responds; recovering the proposal well after its window expires
it and must requeue both participants), confirming both tickets land
back at QUEUED with a refreshed expiry and are visible again to
ListQueuedCandidates. Clean across 5 runs, plus the full integration
and unit suites.

server/store/proposal_recovery_sql_test.go

@@ -17,6 +17,7 @@ func TestProposalRecoverySQLBindsParticipantAndExpiresAtReadBoundary(t *testing.
 		ProposalParticipantRespondSQL:        {"response = 'PENDING'", "responded_at"},
 		ProposalRevisionBumpSQL:              {"revision = revision + 1", "state = 'OPEN'"},
 		ProposalDeclineRequeueSQL:            {"SET state = 'QUEUED'", "state = 'PROPOSED'", "proposal_participants"},
+		ProposalExpireRequeueSQL:             {"SET state = 'QUEUED'", "state = 'PROPOSED'", "state = 'EXPIRED'"},
 	} {
 		for _, fragment := range fragments {
 			if !contains(query, fragment) {