v0.317.0: a second copy counts only on a proven different disk; the no-drive install speaks in words (felhom.eu architecture/16, build A)

Tier-2 and the one-copy notice ask the host agent (POST /disks/same-disk, agent 0.157.0): different +
proven -> made and counted; same disk -> not made (D1); unknown (VM, hidden USB serial) -> made, not
counted, the row says why (D2); a NAS never counts and no longer hides the notice (R-1075). An older
agent keeps the st_dev rule, logged once. D4: a data-folder or media app on a box with no drive is
refused in words with a link to the drives page (R-1068's raw-error half). MinAgent 0.157.0.

Claude-Session: https://claude.ai/code/session_012qRErfCoiTkvDK9N5XHbzb

controller/internal/backup/tier2_shares.go

@@ -177,7 +177,7 @@ func (m *Manager) RunSharesTier2() error {
 		}
 		// Defense-in-depth off-drive guard (selection already enforced it): a leg's target may never
 		// be that leg's own source drive — that would be a same-disk "copy" pretending to be tier 2.
-		if m.sameDevice(g.sourceDrive, target.NamespaceRoot) {
+		if rel, _ := m.diskRelation(g.sourceDrive, target.NamespaceRoot); rel == DiskSame {
 			noTargetWhy = append(noTargetWhy, fmt.Sprintf("%s: a kiválasztott cél ugyanazon a fizikai lemezen van", g.sourceDrive))
 			continue
 		}