feat(config): make listsym_rejected configurable (P2)

The rejected/cancelled checkbox glyph was a hardcoded `const REJECTED = '-'`.
ListSyms now carries a `rejected` field (new_with_rejected); a per-wiki
`listsym_rejected` key (default `-`) is added to WikiConfig, and
WikiConfig::list_syms() builds the palette with it. Routed the three
config-driven ListSyms construction sites (parse path in lib.rs + the
toggle/cycle commands) through list_syms(), so a custom rejected glyph both
lexes and round-trips.

Tests: listsyms::custom_rejected_glyph_is_honoured + config round-trip.
README/doc/lua config comment updated. fmt clean; 0 Rust test failures.

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

crates/nuwiki-core/src/listsyms.rs

@@ -10,32 +10,47 @@
 
 use crate::ast::CheckboxState;
 
+/// Default rejected/cancelled marker (vimwiki's `listsym_rejected`).
 const REJECTED: char = '-';
 
 /// An ordered checkbox progress palette. Always holds at least two glyphs.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ListSyms {
     progression: Vec<char>,
+    rejected: char,
 }
 
 impl Default for ListSyms {
     fn default() -> Self {
         Self {
             progression: " .oOX".chars().collect(),
+            rejected: REJECTED,
         }
     }
 }
 
 impl ListSyms {
-    /// Build a palette from a glyph string. Falls back to the default when
-    /// fewer than two glyphs are supplied (a one-symbol palette can't express
-    /// both "empty" and "done").
+    /// Build a palette from a glyph string, with the default rejected marker.
+    /// Falls back to the default when fewer than two glyphs are supplied (a
+    /// one-symbol palette can't express both "empty" and "done").
     pub fn new(s: &str) -> Self {
+        Self::new_with_rejected(s, REJECTED)
+    }
+
+    /// Like [`new`](Self::new) but with a custom rejected/cancelled glyph
+    /// (vimwiki's `listsym_rejected`).
+    pub fn new_with_rejected(s: &str, rejected: char) -> Self {
         let progression: Vec<char> = s.chars().collect();
         if progression.len() < 2 {
-            Self::default()
+            Self {
+                rejected,
+                ..Self::default()
+            }
         } else {
-            Self { progression }
+            Self {
+                progression,
+                rejected,
+            }
         }
     }
 
@@ -56,7 +71,7 @@ impl ListSyms {
     }
 
     pub fn rejected_glyph(&self) -> char {
-        REJECTED
+        self.rejected
     }
 
     pub fn glyph_at(&self, index: usize) -> char {
@@ -76,7 +91,7 @@ impl ListSyms {
     /// Normalised five-bucket [`CheckboxState`] for a glyph, or `None` when the
     /// glyph is not part of this palette (and is not the rejected marker).
     pub fn state_of(&self, c: char) -> Option<CheckboxState> {
-        if c == REJECTED {
+        if c == self.rejected {
             return Some(CheckboxState::Rejected);
         }
         let index = self.index_of(c)?;
@@ -96,7 +111,7 @@ impl ListSyms {
     /// `ceil` rule, matching the stock five-symbol behaviour.
     pub fn glyph_for_rate(&self, rate: i32) -> char {
         if rate < 0 {
-            return REJECTED;
+            return self.rejected;
         }
         if rate <= 0 {
             return self.empty_glyph();
@@ -157,6 +172,19 @@ mod tests {
         assert_eq!(ListSyms::new("x"), ListSyms::default());
     }
 
+    #[test]
+    fn custom_rejected_glyph_is_honoured() {
+        // `listsym_rejected = '✗'`: that glyph lexes/snaps as Rejected and the
+        // default `-` no longer does.
+        let s = ListSyms::new_with_rejected(" .oOX", '✗');
+        assert_eq!(s.rejected_glyph(), '✗');
+        assert_eq!(s.state_of('✗'), Some(CheckboxState::Rejected));
+        assert_eq!(s.glyph_for_rate(-1), '✗');
+        assert_eq!(s.state_of('-'), None); // no longer the rejected marker
+                                           // A short palette still keeps the custom rejected glyph.
+        assert_eq!(ListSyms::new_with_rejected("x", '✗').rejected_glyph(), '✗');
+    }
+
     #[test]
     fn custom_palette_buckets_to_nearest_state() {
         // 3 glyphs → rates 0 / 50 / 100.