feat(viewer): present subtitles, fonts, PNG + text in the PAK browser

Decode and present four more PAK item types in the pack browser's detail
pane. All content is decoded off-thread in build_pak_rows and attached to
each PakRow, then rendered with egui's own texture facilities — the Bevy
texture pipeline and egui's global font system are untouched.

formats crate (Bevy-free, reusable by CLI):
- ixud: parse IXUD localized-string tables as subtitle cue lists (UTF-16BE
  pool, SUBTITLE header + (text, timecode) pairs -> Vec<Cue{start,end,text}>).
- font: OTF/TTF/ttcf metadata (family / faces / glyphs) via ttf-parser.

viewer:
- PakRow gains `content: PakContent` (Subtitle | Font | Png | Text | None);
  classify_content fills it for IXUD / fonts / PNG / xml+text within the
  existing decode budget. Font samples are pre-rasterized off-thread with
  ab_glyph into an image (ImageRgba) — ab_glyph returns Option/Result at every
  step, so a bad font yields no sample instead of panicking (the earlier
  egui set_fonts approach crashed the app on atlas rebuild).
- draw_pak_browser dispatches on content: subtitle cue table, font metadata +
  sample image, PNG image, scrollable text; else the existing IDXD detail.
  Borrow-split PakView instead of cloning the (now heavy) rows each frame;
  one hash-keyed egui texture cache serves both PNG and font-sample images.

Subtitle<->movie auto-matching is deferred: movie filenames don't hash to the
IXUD keys and no cross-reference table was found (the link is an internal
MSG_DEMO id), so the movie player gets no subtitle track yet.

Tests: ixud unit tests; disc tests for the real English subtitle track
(cues + timecodes), eng/deu localization, font metadata, and off-thread
rasterization of the real font.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/sylpheed-formats/src/font.rs

@@ -0,0 +1,64 @@
+//! Font metadata for the embedded UI fonts.
+//!
+//! The packs carry sfnt fonts (`\x00\x01\x00\x00` TrueType, `OTTO` OpenType/CFF)
+//! and TrueType Collections (`ttcf`). We only need light metadata to *present*
+//! them — family name, face count, glyph count — which `ttf-parser` extracts
+//! safely (malformed input yields `None`, never a panic). The raw bytes are
+//! handed to egui separately for a live sample.
+
+use ttf_parser::{fonts_in_collection, name_id, Face};
+
+/// Light font metadata for the viewer.
+#[derive(Debug, Clone, PartialEq)]
+pub struct FontInfo {
+    /// "TrueType", "OpenType (CFF)", or "TrueType Collection".
+    pub kind: &'static str,
+    /// Family / full name (best-effort; empty if the name table is unreadable).
+    pub family: String,
+    /// Number of faces (1 for a plain sfnt, N for a `ttcf` collection).
+    pub faces: u32,
+    /// Glyph count of the first face.
+    pub glyphs: u16,
+}
+
+/// Whether `bytes` starts with a recognized font signature.
+pub fn is_font(bytes: &[u8]) -> bool {
+    matches!(
+        bytes.get(0..4),
+        Some(b"\x00\x01\x00\x00") | Some(b"OTTO") | Some(b"true") | Some(b"ttcf")
+    )
+}
+
+/// Extract light metadata, or `None` if the font can't be parsed.
+pub fn parse_info(bytes: &[u8]) -> Option<FontInfo> {
+    let is_collection = bytes.get(0..4) == Some(b"ttcf");
+    let faces = fonts_in_collection(bytes).unwrap_or(1).max(1);
+
+    // Face 0 gives the representative family + glyph count.
+    let face = Face::parse(bytes, 0).ok()?;
+    let glyphs = face.number_of_glyphs();
+
+    let kind = if is_collection {
+        "TrueType Collection"
+    } else if bytes.get(0..4) == Some(b"OTTO") {
+        "OpenType (CFF)"
+    } else {
+        "TrueType"
+    };
+
+    // Prefer the typographic/full family name; fall back to any readable name.
+    let family = face
+        .names()
+        .into_iter()
+        .filter(|n| n.name_id == name_id::FULL_NAME || n.name_id == name_id::FAMILY)
+        .find_map(|n| n.to_string())
+        .or_else(|| face.names().into_iter().find_map(|n| n.to_string()))
+        .unwrap_or_default();
+
+    Some(FontInfo {
+        kind,
+        family,
+        faces,
+        glyphs,
+    })
+}