Round 3: fix three defects introduced by the round-2 fixes

Auditing my own fixes found all three. None were in the original code.

The VTS crack sort was byte-wise case-SENSITIVE while the filters that select
those files (vts_group_of / is_title_vob) are case-insensitive. On a
case-sensitive volume a set holding vts_01_1.vob beside VTS_01_2.VOB sorted
part 2 first, because V (0x56) precedes v (0x76) — reintroducing exactly the
budget-exhaustion the ordering exists to prevent. Now sorted on the same
uppercase normalisation the filters apply.

Refusing a name that round-trips to empty aborted the WHOLE plan. A sidecar
folder named with a single emoji made a backup un-rippable that 1.6.0 handled
fine, and reported it as a collision with a file that does not exist. It is now
skipped with a warning: the entry is unaddressable either way, but one
irrelevant file should not cost the user their rip.

The mtime check now applies only to files whose CONTENT the plan read — the
IFOs, whose bytes 0xC0/0xC4 place every VOB. Everything else is planned from
size alone, which is already checked, so comparing mtime there bought nothing
and risked a real false positive: disc backups commonly live on exFAT/FAT32,
which stores local time, so a long rip spanning a DST transition would see a
whole-hour shift on an untouched multi-gigabyte VOB and abort hours in.

src/disc/extract.rs

@@ -318,7 +318,13 @@ impl Disc {
                 vts_group_of(&pf.disc_name).as_deref() == Some(vts) && is_title_vob(&pf.disc_name)
             })
             .collect();
-        files.sort_by(|a, b| a.disc_name.cmp(&b.disc_name));
+        // Case-INSENSITIVE, matching `vts_group_of`/`is_title_vob`, which
+        // selected these files case-insensitively. A byte-wise sort put
+        // 'V' (0x56) before 'v' (0x76), so a set holding `vts_01_1.vob`
+        // alongside `VTS_01_2.VOB` — reachable on a case-sensitive volume —
+        // started the crack at part 2 and could exhaust the budget in a clear
+        // run, which is the whole failure this ordering exists to prevent.
+        files.sort_by_key(|f| f.disc_name.to_ascii_uppercase());
 
         let mut extents: Vec<crate::disc::Extent> = Vec::new();
         for pf in files {