feat(tui): Phase 2 Issue List + MR List screens

Implement state, action, and view layers for both list screens:
- Issue List: keyset pagination, snapshot fence, filter DSL, label aggregation
- MR List: mirrors Issue pattern with draft/reviewer/target branch filters
- Migration 027: covering indexes for TUI list screen queries
- Updated Msg types to use typed Page structs instead of raw Vec<Row>
- 303 tests passing, clippy clean

Beads: bd-3ei1, bd-2kr0, bd-3pm2

crates/lore-tui/src/navigation.rs

@@ -60,9 +60,10 @@ impl NavigationStack {
         self.forward_stack.clear();
 
         // Record significant hops in jump list (vim behavior):
-        // truncate any forward entries beyond jump_index, then append.
+        // Keep entries up to and including the current position, discard
+        // any forward entries beyond it, then append the new destination.
         if self.current.is_detail_or_entity() {
-            self.jump_list.truncate(self.jump_index);
+            self.jump_list.truncate(self.jump_index.saturating_add(1));
             self.jump_list.push(self.current.clone());
             self.jump_index = self.jump_list.len();
         }
@@ -90,23 +91,37 @@ impl NavigationStack {
 
     /// Jump backward through the jump list (vim Ctrl+O).
     ///
-    /// Only visits detail/entity screens.
+    /// Only visits detail/entity screens. Skips entries matching the
+    /// current screen so the first press always produces a visible change.
     pub fn jump_back(&mut self) -> Option<&Screen> {
-        if self.jump_index == 0 {
-            return None;
+        while self.jump_index > 0 {
+            self.jump_index -= 1;
+            if let Some(target) = self.jump_list.get(self.jump_index).cloned()
+                && target != self.current
+            {
+                self.current = target;
+                return Some(&self.current);
+            }
         }
-        self.jump_index -= 1;
-        self.jump_list.get(self.jump_index)
+        None
     }
 
     /// Jump forward through the jump list (vim Ctrl+I).
+    ///
+    /// Skips entries matching the current screen.
     pub fn jump_forward(&mut self) -> Option<&Screen> {
-        if self.jump_index >= self.jump_list.len() {
-            return None;
+        while self.jump_index < self.jump_list.len() {
+            if let Some(target) = self.jump_list.get(self.jump_index).cloned() {
+                self.jump_index += 1;
+                if target != self.current {
+                    self.current = target;
+                    return Some(&self.current);
+                }
+            } else {
+                break;
+            }
         }
-        let screen = self.jump_list.get(self.jump_index)?;
-        self.jump_index += 1;
-        Some(screen)
+        None
     }
 
     /// Reset to a single screen, clearing all history.
@@ -246,24 +261,21 @@ mod tests {
         nav.push(Screen::MrList);
         nav.push(mr.clone());
 
-        // jump_index is at 2 (past the end of 2 items)
-        let prev = nav.jump_back();
-        assert_eq!(prev, Some(&mr));
-
+        // Current is MrDetail. jump_list = [IssueDetail, MrDetail], index = 2.
+        // First jump_back skips MrDetail (== current) and lands on IssueDetail.
         let prev = nav.jump_back();
         assert_eq!(prev, Some(&issue));
+        assert!(nav.is_at(&issue));
 
-        // at beginning
+        // Already at beginning of jump list.
         assert!(nav.jump_back().is_none());
 
-        // forward
-        let next = nav.jump_forward();
-        assert_eq!(next, Some(&issue));
-
+        // jump_forward skips IssueDetail (== current) and lands on MrDetail.
         let next = nav.jump_forward();
         assert_eq!(next, Some(&mr));
+        assert!(nav.is_at(&mr));
 
-        // at end
+        // At end of jump list.
         assert!(nav.jump_forward().is_none());
     }
 
@@ -274,10 +286,9 @@ mod tests {
         nav.push(Screen::IssueDetail(EntityKey::issue(1, 2)));
         nav.push(Screen::IssueDetail(EntityKey::issue(1, 3)));
 
-        // jump back twice
+        // jump back twice — lands on issue(1,1), jump_index = 0
         nav.jump_back();
         nav.jump_back();
-        // jump_index = 1, pointing at issue 2
 
         // new detail push truncates forward entries
         nav.push(Screen::MrDetail(EntityKey::mr(1, 99)));