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/commands/defs.rs

@@ -0,0 +1,180 @@
+//! Command definitions — types for keybindings, screen filtering, and command metadata.
+
+use ftui::{KeyCode, Modifiers};
+
+use crate::message::Screen;
+
+// ---------------------------------------------------------------------------
+// Key formatting
+// ---------------------------------------------------------------------------
+
+/// Format a key code + modifiers as a human-readable string.
+pub(crate) fn format_key(code: KeyCode, modifiers: Modifiers) -> String {
+    let mut parts = Vec::new();
+    if modifiers.contains(Modifiers::CTRL) {
+        parts.push("Ctrl");
+    }
+    if modifiers.contains(Modifiers::ALT) {
+        parts.push("Alt");
+    }
+    if modifiers.contains(Modifiers::SHIFT) {
+        parts.push("Shift");
+    }
+    let key_name = match code {
+        KeyCode::Char(c) => c.to_string(),
+        KeyCode::Enter => "Enter".to_string(),
+        KeyCode::Escape => "Esc".to_string(),
+        KeyCode::Tab => "Tab".to_string(),
+        KeyCode::Backspace => "Backspace".to_string(),
+        KeyCode::Delete => "Del".to_string(),
+        KeyCode::Up => "Up".to_string(),
+        KeyCode::Down => "Down".to_string(),
+        KeyCode::Left => "Left".to_string(),
+        KeyCode::Right => "Right".to_string(),
+        KeyCode::Home => "Home".to_string(),
+        KeyCode::End => "End".to_string(),
+        KeyCode::PageUp => "PgUp".to_string(),
+        KeyCode::PageDown => "PgDn".to_string(),
+        KeyCode::F(n) => format!("F{n}"),
+        _ => "?".to_string(),
+    };
+    parts.push(&key_name);
+    // We need to own the joined string.
+    let joined: String = parts.join("+");
+    joined
+}
+
+// ---------------------------------------------------------------------------
+// KeyCombo
+// ---------------------------------------------------------------------------
+
+/// A keybinding: either a single key or a two-key sequence.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub enum KeyCombo {
+    /// Single key press (e.g., `q`, `Esc`, `Ctrl+P`).
+    Single { code: KeyCode, modifiers: Modifiers },
+    /// Two-key sequence (e.g., `g` then `i` for go-to-issues).
+    Sequence {
+        first_code: KeyCode,
+        first_modifiers: Modifiers,
+        second_code: KeyCode,
+        second_modifiers: Modifiers,
+    },
+}
+
+impl KeyCombo {
+    /// Convenience: single key with no modifiers.
+    #[must_use]
+    pub const fn key(code: KeyCode) -> Self {
+        Self::Single {
+            code,
+            modifiers: Modifiers::NONE,
+        }
+    }
+
+    /// Convenience: single key with Ctrl modifier.
+    #[must_use]
+    pub const fn ctrl(code: KeyCode) -> Self {
+        Self::Single {
+            code,
+            modifiers: Modifiers::CTRL,
+        }
+    }
+
+    /// Convenience: g-prefix sequence (g + char).
+    #[must_use]
+    pub const fn g_then(c: char) -> Self {
+        Self::Sequence {
+            first_code: KeyCode::Char('g'),
+            first_modifiers: Modifiers::NONE,
+            second_code: KeyCode::Char(c),
+            second_modifiers: Modifiers::NONE,
+        }
+    }
+
+    /// Human-readable display string for this key combo.
+    #[must_use]
+    pub fn display(&self) -> String {
+        match self {
+            Self::Single { code, modifiers } => format_key(*code, *modifiers),
+            Self::Sequence {
+                first_code,
+                first_modifiers,
+                second_code,
+                second_modifiers,
+            } => {
+                let first = format_key(*first_code, *first_modifiers);
+                let second = format_key(*second_code, *second_modifiers);
+                format!("{first} {second}")
+            }
+        }
+    }
+
+    /// Whether this combo starts with the given key.
+    #[must_use]
+    pub fn starts_with(&self, code: &KeyCode, modifiers: &Modifiers) -> bool {
+        match self {
+            Self::Single {
+                code: c,
+                modifiers: m,
+            } => c == code && m == modifiers,
+            Self::Sequence {
+                first_code,
+                first_modifiers,
+                ..
+            } => first_code == code && first_modifiers == modifiers,
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// ScreenFilter
+// ---------------------------------------------------------------------------
+
+/// Specifies which screens a command is available on.
+#[derive(Debug, Clone)]
+pub enum ScreenFilter {
+    /// Available on all screens.
+    Global,
+    /// Available only on specific screens.
+    Only(Vec<Screen>),
+}
+
+impl ScreenFilter {
+    /// Whether the command is available on the given screen.
+    #[must_use]
+    pub fn matches(&self, screen: &Screen) -> bool {
+        match self {
+            Self::Global => true,
+            Self::Only(screens) => screens.contains(screen),
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// CommandDef
+// ---------------------------------------------------------------------------
+
+/// Unique command identifier.
+pub type CommandId = &'static str;
+
+/// A registered command with its keybinding, help text, and scope.
+#[derive(Debug, Clone)]
+pub struct CommandDef {
+    /// Unique identifier (e.g., "quit", "go_issues").
+    pub id: CommandId,
+    /// Human-readable label for palette and help overlay.
+    pub label: &'static str,
+    /// Keybinding (if any).
+    pub keybinding: Option<KeyCombo>,
+    /// Equivalent `lore` CLI command (for "Show CLI equivalent" feature).
+    pub cli_equivalent: Option<&'static str>,
+    /// Description for help overlay.
+    pub help_text: &'static str,
+    /// Short hint for status bar (e.g., "q:quit").
+    pub status_hint: &'static str,
+    /// Which screens this command is available on.
+    pub available_in: ScreenFilter,
+    /// Whether this command works in Text input mode.
+    pub available_in_text_mode: bool,
+}