re(challenge): poking unlocks the whole story campaign; MISSION SELECT is story-only

Two results from the running game, one positive and one a clean negative.

POSITIVE: with word A = 0x0001FFFE (stages 1-16) every entry Stage01..Stage16 is
selectable, where the control run had only Stage01 and the rest greyed. Stage16
reads "Lonely Blue Planet - NO RECORD". So any story stage can be launched from
the menu by poking one word, with no save editing at all -- a simpler lever than
the GHAD stage-field patch used until now.

NEGATIVE: with word B = 0x3F (challenge stages 24-29 marked cleared) the list
still saturates at Stage16 -- the cursor stops there and further presses do
nothing. That matches the disc: the debriefing config declares exactly
px_deb_stage01..16, so the list is capped by data, not by the mask. The
challenge missions are NOT reachable through MISSION SELECT, and word B does not
feed it.

Also mapped, without finding the caller: the GP_DIALOG registry (tables.pak #41)
gives DLG_GO_CHALLENGE_MISSION_MENU = 41 and DLG_CHALLENGE_MISSION_AVAILABLE = 42
(0-based, in config order). No raw immediate 41/39/37 appears anywhere in the
GamePart code region, so dialogs are raised through a computed index and the
entry point to GamePart 26 is still unknown. New probe: examples/screen_configs.rs
dumps any tables.pak screen config by substring.

crates/sylpheed-formats/examples/screen_configs.rs

@@ -0,0 +1,18 @@
+//! RE probe: dump tables.pak screen-config records that mention a given token.
+//! Usage: screen_configs <disc-root> <substring>
+use sylpheed_formats::{idxd::IdxdObject, pak::PakArchive};
+fn main(){
+    let a:Vec<String>=std::env::args().collect();
+    let needle=a.get(2).cloned().unwrap_or_else(||"CHALLENGE".into());
+    let arc=PakArchive::open(format!("{}/dat/tables.pak",a[1])).unwrap();
+    for (i,e) in arc.entries().iter().enumerate(){
+        let Ok(b)=arc.read(e) else{continue};
+        let Ok(o)=IdxdObject::parse(&b) else{continue};
+        let t=o.tokens();
+        if !t.iter().any(|s|s.to_lowercase().contains(&needle.to_lowercase())){continue}
+        let path=t.iter().find(|s|s.contains(".pak+")).cloned().unwrap_or_default();
+        if !path.is_empty() && !path.contains("+eng"){continue}
+        println!("\n=== entry #{i} schema {:08x} [{path}] {} tokens ===",o.schema_hash,t.len());
+        for (j,tok) in t.iter().enumerate(){println!("  {j:3}  {tok}");}
+    }
+}