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/state/mod.rs

@@ -24,7 +24,7 @@ pub mod sync;
 pub mod timeline;
 pub mod who;
 
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 
 use crate::message::Screen;
 
@@ -80,6 +80,8 @@ impl LoadState {
 #[derive(Debug, Default)]
 pub struct ScreenLoadStateMap {
     map: HashMap<Screen, LoadState>,
+    /// Screens that have had a load state set at least once.
+    visited: HashSet<Screen>,
 }
 
 impl ScreenLoadStateMap {
@@ -94,6 +96,7 @@ impl ScreenLoadStateMap {
     ///
     /// Setting to `Idle` removes the entry to prevent map growth.
     pub fn set(&mut self, screen: Screen, state: LoadState) {
+        self.visited.insert(screen.clone());
         if state == LoadState::Idle {
             self.map.remove(&screen);
         } else {
@@ -101,6 +104,12 @@ impl ScreenLoadStateMap {
         }
     }
 
+    /// Whether this screen has ever had a load initiated.
+    #[must_use]
+    pub fn was_visited(&self, screen: &Screen) -> bool {
+        self.visited.contains(screen)
+    }
+
     /// Whether any screen is currently loading.
     #[must_use]
     pub fn any_loading(&self) -> bool {