fix(scanner): repair acronym and apostrophe casing on genre tags — #2468

Operator decision: keep the ID3v1 table canonical, fix the casing.

The operator's library carries "Edm", "Idm", "Aor", "Uk Garage", "Uk
Hardcore", "Trap Edm", "Glitch Hop Edm" and "Children'S Music" — an external
tag editor title-cased the whole genre field. The "'S" is the giveaway.

Fixed at SCAN time, not in the display layer: taste_profile.sql reads
tracks.genre directly, so a cosmetic-only fix would leave the taste
vocabulary holding "Edm" while the UI showed "EDM", and any correctly
tagged file would contribute a second, separate tag.

trueUpCasing only ever changes case, never letters, so it cannot silently
turn one genre into a different one — that is what separates it from the
label-remapping idea this task rejected. Two narrow rules:

- A short, evidence-led acronym list, matched case-insensitively so "edm",
  "Edm" and "EDM" all land on "EDM". This is a deliberate exception to the
  project's rule that genre case is exposed as the file says it: "Rock" and
  "rock" still stay separate rows, because folding those is a judgement about
  labels, whereas there is no genre named "Edm".
- Apostrophe suffixes from a FIXED contraction list, so "Children'S" is
  repaired while "O'Brien" and "D'Angelo" keep their capital. A blanket
  "lowercase after an apostrophe" would have broken both.

Matching uses the word's letter core rather than the raw word, so "(Edm)"
and "Edm," are repaired and their punctuation re-attached. Interior
punctuation stays in the core, so "Lo-Fi" and "R&B" are compared whole and
cannot match a fragment by accident. My first version missed this and a test
expecting "(Live EDM)" caught it.

Names resolved from the ID3v1 table are deliberately NOT re-cased, per the
operator's call — entry 40's "AlternRock" stays as the table spells it, with
a test pinning that so a later tidy-up doesn't quietly "fix" it.

tagReadVersion 1 -> 2, so this reaches the existing library on the next scan
rather than new files only. That re-read reuses stored durations, so it costs
tag reads and no ffprobe.

internal/library/scanner.go

@@ -52,7 +52,11 @@ var audioExtensions = map[string]bool{
 //	   ("Alternative Rock" + "Rock" -> "Alternative RockRock"), which corrupted
 //	   the genre browse axis and polluted the taste profile's tag vocabulary,
 //	   and left bare ID3v1 numeric references unresolved (#2499).
-const tagReadVersion int16 = 1
+//	2: acronym and apostrophe casing repaired on genre values (#2468) — "Edm" ->
+//	   "EDM", "Children'S Music" -> "Children's Music". Bumped rather than left
+//	   to new files only because taste_profile.sql reads tracks.genre directly,
+//	   so a half-repaired library would carry both spellings as separate tags.
+const tagReadVersion int16 = 2
 
 type Stats struct {
 	Scanned int `json:"scanned"`