localization: resolve the game's UTF-16 text keys to display strings

Project Sylpheed stores its UI/story text in IXUD entries as UTF-16LE,
interleaved `text, key` (a prose string immediately followed by the
identifier that names it). TextIndex::build(pak) scans a language pak's
IXUD entries and indexes every pair — 8457 English keys from
GP_MAIN_GAME_E: objectives, hints, lose conditions, character names,
and cutscene dialogue.

This makes the whole game read in English: the 16-mission campaign
(Repel the surprise attack → Shoot down Margras → the Prometheus Driver
finale), each mission's briefing, and the named cast (Katana, Raymond,
Ellen, Crichton, …) all resolve. API: get / objectives / lose_conditions
/ hints / character_name. 3 tests.

Examples: campaign / dossier print the readable campaign + cast.

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

crates/sylpheed-formats/examples/campaign.rs

@@ -0,0 +1,24 @@
+use sylpheed_formats::{game_data, localization::TextIndex, PakArchive};
+fn main(){
+    let disc=std::env::var("SYLPHEED_DISC").unwrap();
+    let pak=PakArchive::open(format!("{disc}/dat/GP_MAIN_GAME_E.pak")).unwrap();
+    let text=TextIndex::build(&pak);
+    let mut stages=game_data::load_stages(&pak);
+    stages.retain(|s|s.id.starts_with('S') && s.id.len()==3 && s.id[1..].parse::<u32>().map(|n|n<=16).unwrap_or(false));
+    stages.sort_by(|a,b|a.id.cmp(&b.id));
+    println!("═══ CAMPAIGN (S01–S16) ═══");
+    for s in &stages{
+        let obj=text.objectives(&s.id,1);
+        println!("\n{} · {}", s.id, s.location.as_deref().unwrap_or("?"));
+        for o in obj.iter().take(2){ println!("   ▸ {o}"); }
+    }
+    // roster with real names
+    let mut chars=game_data::load_characters(&pak);
+    chars.retain(|c|c.faction.as_deref()==Some("TCAF") && c.unique==Some(true) && c.faces.len()>=4);
+    println!("\n═══ PRINCIPAL CAST (TCAF, named) ═══");
+    for c in &chars{
+        let id=c.id.as_deref().unwrap_or("");
+        let name=text.character_name(id.trim_start_matches("Character")).or_else(||c.name_key.as_deref().and_then(|k|text.get(k))).unwrap_or("?");
+        println!("   {name:12} ({} portraits)  [{}]", c.faces.len(), id.trim_start_matches("Character"));
+    }
+}

crates/sylpheed-formats/examples/dossier.rs

@@ -0,0 +1,15 @@
+use sylpheed_formats::{game_data, localization::TextIndex, PakArchive};
+fn main(){
+    let disc=std::env::var("SYLPHEED_DISC").unwrap();
+    let pak=PakArchive::open(format!("{disc}/dat/GP_MAIN_GAME_E.pak")).unwrap();
+    let text=TextIndex::build(&pak);
+    for n in 1..=16u32{
+        let sid=format!("S{n:02}");
+        // primary objective across phases (first that resolves)
+        let obj:Vec<String>=(1..=3).flat_map(|p|text.objectives(&sid,p)).map(|s|s.to_string()).collect();
+        let lose:Vec<String>=(1..=3).flat_map(|p|text.lose_conditions(&sid,p)).map(|s|s.to_string()).collect();
+        let full_obj=obj.join(" ");
+        let full_lose=lose.into_iter().take(2).collect::<Vec<_>>().join(" ");
+        println!("{sid}\t{full_obj}\t{full_lose}");
+    }
+}