refactor: add Keymap with default bindings and wire into handle_key

Create keymap.rs with Keymap struct mapping (mode, key) to Cmd trait
objects. Wire into App::handle_key — keymap dispatch is tried first,
falling through to old handlers for unmigrated bindings. Normal mode
navigation, cell ops, mode switches, and Help mode are keymap-driven.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ui/app.rs

@@ -3,6 +3,8 @@ use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
 use std::path::{Path, PathBuf};
 use std::time::{Duration, Instant};
 
+use crate::command::cmd::CmdContext;
+use crate::command::keymap::Keymap;
 use crate::command::{self, Command};
 use crate::import::wizard::{ImportWizard, WizardStep};
 use crate::model::cell::{CellKey, CellValue};
@@ -66,6 +68,7 @@ pub struct App {
     pub pending_key: Option<char>,
     /// Yanked cell value for `p` paste
     pub yanked: Option<CellValue>,
+    keymap: Keymap,
 }
 
 impl App {
@@ -88,6 +91,23 @@ impl App {
             dirty: false,
             pending_key: None,
             yanked: None,
+            keymap: Keymap::default_keymap(),
+        }
+    }
+
+    fn cmd_context(&self) -> CmdContext {
+        let view = self.model.active_view();
+        CmdContext {
+            model: &self.model,
+            mode: &self.mode,
+            selected: view.selected,
+            row_offset: view.row_offset,
+            col_offset: view.col_offset,
+            search_query: &self.search_query,
+            yanked: &self.yanked,
+            pending_key: self.pending_key,
+            dirty: self.dirty,
+            file_path_set: self.file_path.is_some(),
         }
     }
 
@@ -103,9 +123,19 @@ impl App {
     }
 
     pub fn handle_key(&mut self, key: KeyEvent) -> Result<()> {
+        // Try keymap first — if a binding matches, apply effects and return
+        let ctx = self.cmd_context();
+        if let Some(effects) = self.keymap.dispatch(&ctx, key.code, key.modifiers) {
+            drop(ctx);
+            self.apply_effects(effects);
+            return Ok(());
+        }
+        drop(ctx);
+
         match &self.mode.clone() {
             AppMode::Quit => {}
             AppMode::Help => {
+                // Handled by keymap now, but keep as fallback
                 self.mode = AppMode::Normal;
             }
             AppMode::ImportWizard => {