unlock: add Unlocker::name() + report-only applies_to() for the matrix

Each unlocker now carries its own stable name() (the single source; apps
never hardcode it) and a report-only applies_to() — phase-independent
'would this apply to this drive+disc', distinct from the dispatch-gated
matches(). LibreDrive overrides applies_to to report on drive identity
regardless of disc kind (its matches() is gated to the Unknown-kind init
phase). Enables a registry-driven unlocker matrix.

src/css/mod.rs

@@ -160,6 +160,10 @@ impl Default for CssUnlocker {
 }
 
 impl crate::Unlocker for CssUnlocker {
+    fn name(&self) -> &'static str {
+        "CSS"
+    }
+
     fn matches(&self, ctx: &crate::UnlockCtx) -> bool {
         ctx.kind == crate::DiscKind::Css
     }