feat: resolve conflicts through focused two-way drafts

Replace the marker-filled three-pane resolver with a marker-free native
Draft versus frozen Alternative projected from current working text.
Preserve preexisting outside edits, native undo, dirty-save guards, all
sides/bases, and draft caret/viewports across separate History views.
Reuse DiffState alignment/highlighting/excerpts for Resolution and merge
its base-aligned rows for readonly three-way History. Hide explorer and
source-selector chrome by default.

Verified 926 tests plus actual terminal projection, History highlighting,
hunk choice, optional explorer, and guarded jj-confirmed save workflows.
Clippy completes with pre-existing warnings only. Smoke fixtures stay
unresolved in this ancestry; remove that ancestry before publication.

Size exception: approximately 1650 implementation added/deleted lines,
excluding tests/docs, kept coherent because native draft lifecycle and
aligned rendering must change together without parallel legacy modes.

tests/resolve.rs

@@ -146,7 +146,10 @@ fn resolver_keeps_unsaved_result_and_undo_then_saves_and_retains_resolved_file()
     ]);
     session.execute("resolve");
     ready(&mut session);
-    assert_eq!(session.editor().context().text, draft);
+    let seeded = format!("draft\n{}", Fixture::text("left"));
+    assert_eq!(session.editor().context().text, seeded);
+    assert_ne!(seeded, draft);
+    assert!(session.editor().dirty());
     assert_eq!(
         fs::read_to_string(fixture.root.join("first.txt")).unwrap(),
         original_disk
@@ -164,23 +167,33 @@ fn resolver_keeps_unsaved_result_and_undo_then_saves_and_retains_resolved_file()
         ]),
         operation
     );
+    session.handle(Input::Char('u'));
+    assert_eq!(session.editor().context().text, draft);
+    session.handle(Input::Char('U'));
+    assert_eq!(session.editor().context().text, seeded);
     let source = session.editor().resolver().unwrap().files[0]
         .sources
         .iter()
-        .position(|source| !source.base)
+        .enumerate()
+        .filter(|(_, source)| !source.base)
+        .nth(1)
         .unwrap()
+        .0
         + 1;
     session.execute(&format!("resolve.use_source {source}"));
-    assert_ne!(session.editor().context().text, draft);
-    assert!(session.editor().context().text.starts_with("draft\n"));
+    let chosen = session.editor().context().text;
+    assert_ne!(chosen, seeded);
+    assert!(chosen.starts_with("draft\n"));
+    assert!(chosen.contains("context_15\n"));
     session.handle(Input::Char('u'));
-    assert_eq!(session.editor().context().text, draft);
-    session.execute(&format!("resolve.use_source {source}"));
-    session.execute("resolve.next");
+    assert_eq!(session.editor().context().text, seeded);
     session.execute(&format!("resolve.use_source {source}"));
+    let cursor = session.editor().cursor();
     let resolved_text = session.editor().context().text;
-    assert!(resolved_text.starts_with("draft\n"));
-    assert!(resolved_text.contains("context_15\n"));
+    session.execute("resolve.view.toggle");
+    session.execute("resolve.view.toggle");
+    assert_eq!(session.editor().context().text, resolved_text);
+    assert_eq!(session.editor().cursor(), cursor);
     session.execute("w");
     ready(&mut session);
     let resolver = session.editor().resolver().unwrap();