Cutscene voice: resolve movies via continuous-stream cue regions

Cracked how the game maps a movie to its voice track and reimplemented it,
fixing wrong/short voices for RT and hokyu cutscenes.

## Mechanism (RE'd from a Canary file-I/O trace, user-confirmed by ear)

The movie voices are ONE continuous XMA stream, physically chunked into
`<lang>\Movie\VOICE_*.slb` (and `\etc\VOICE_D_*.slb`) sound.pak TOC entries
whose boundaries do NOT align with the cutscene cues. A single cue routinely
spans two `.slb` chunks, so a `.slb` does not necessarily hold the track its
name claims (they are off-by-one vs the cues). Each cue ends at an inline
trailer descriptor `(sound_id:u32be, 0x11, …)` whose id repeats at +0x800.

Resolution chain (all derivable on-disc, no guest-code RE):
  1. movie -> cue token         (ADVERTISE_MOVIE manifest VOICETRACK)
  2. cue token -> sound-id       (master sound registry, tables.pak
                                  a2c8c185=eng / b04238e0=jpn, schema 0x13cb84ba)
  3. sound-id -> [start,end)      scan the stream for trailer(id) and its
                                  predecessor; cue audio = the bytes between,
                                  read continuously across chunk boundaries.

Validated: decoded voice length matches each movie within ~0.4s, including
cross-boundary cues (ADV/RT01A/RT01B/RT01C/S00A/S01A + the 5 bound hokyu).

## Changes

- sylpheed-formats/src/movie_voice.rs (new): registry_voice_ids(),
  find_descriptor(), find_descriptor_before() (gap-tolerant predecessor).
  Unit-tested.
- viewer iso_loader.rs: resolve_movie_voice_region() + decode_voice_region()
  (continuous read via existing read_segment_range + to_xma_riffs). Voice/
  audio requests now region-first; a `\Movie\` token that fails region stays
  SILENT (never plays the wrong off-by-one chunk). Removed the old
  movie_is_demo_based suppress hack.
- Anchor tries subdirs Movie/etc/Voice so hokyu `\etc\VOICE_D_*` resolve too.
- Examples resolve_all/validate_cues/hokyu_final document + validate the pipeline.

## Status

- RT / S / ADV cutscene voices: CORRECT (user-confirmed).
- 5 manifest-bound hokyu (VOICE_D_450-454): CORRECT (user-confirmed).

## OPEN (handoff)

13 of 18 hokyu movies have NO manifest VOICETRACK; the game reuses the 5
recordings across stages via a code rule. `hokyu_fallback_token()` currently
guesses by category (ship LS/DS x source carrier-A/tanker-H: LS/A->450,
LS/H->453, DS/A->452, DS/H->454). USER REPORTS THIS IS SOMETIMES WRONG.
- LS/carrier has two takes (450 from s02A, 451 from s09A); the early-vs-late
  split is unknown — unbound LS/A currently all default to 450.
- Definitive fix = Canary `--phase_a_fileio_only` file.read trace of an unbound
  hokyu (e.g. hokyu_LS_s03A) to see which VOICE_D the game actually streams,
  then encode the real rule. Same method that cracked the RT mapping.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/sylpheed-formats/src/slb.rs

@@ -200,6 +200,38 @@ pub fn to_xma_riff(slb: &[u8]) -> Option<Vec<u8>> {
     }
 }
 
+/// Rebuild a standalone XMA1 `RIFF/WAVE` from a single-stream `.slb`, robust to
+/// the layout variants seen in `<lang>\etc\` radio clips. Unlike [`to_xma_riff`]
+/// (which assumes `RIFF → fmt → data` in order), this picks the **largest `data`
+/// chunk anywhere** in the bank — some radio banks store the audio *before* the
+/// trailing `RIFF`/`fmt` metadata (an empty post-`RIFF` `data` chunk), which the
+/// ordered scan misses. Pairs it with the first `fmt ` chunk; falls back to the
+/// headerless layout. Returns `None` only when no usable audio can be found.
+pub fn to_xma_riff_best(slb: &[u8]) -> Option<Vec<u8>> {
+    // Largest usable `data` chunk (bounded by its declared size and the buffer).
+    let mut best: Option<(usize, usize)> = None; // (data offset, usable payload len)
+    let mut i = 0;
+    while let Some(di) = find(slb, b"data", i) {
+        let declared = le32(slb, di + 4).unwrap_or(0) as usize;
+        let usable = declared.min(slb.len().saturating_sub(di + 8));
+        if best.map_or(true, |(_, b)| usable > b) {
+            best = Some((di, usable));
+        }
+        i = di + 4;
+    }
+    if let (Some(fi), Some((di, sz))) = (find(slb, b"fmt ", 0), best) {
+        if sz > 512 {
+            let fsz = le32(slb, fi + 4)? as usize;
+            let fmt_end = (fi + 8 + fsz).min(slb.len());
+            let data = slb.get(di + 8..di + 8 + sz)?;
+            return Some(build_riff(slb.get(fi..fmt_end)?, data));
+        }
+    }
+    // Headerless fallback: fixed data offset, synthesized XMA1 stereo/48k fmt.
+    let data = slb.get(HEADERLESS_DATA_OFFSET..)?;
+    (!data.is_empty()).then(|| build_riff(&synth_xma1_fmt(2, 2, 48000), data))
+}
+
 /// A minimal `fmt ` chunk carrying an XMA1 `XMAWAVEFORMAT` (one stream).
 fn synth_xma1_fmt(channels: u8, channel_mask: u16, rate: u32) -> Vec<u8> {
     let mut fmt = Vec::with_capacity(40);