test(peer-cli): expand streamed install edge coverage

NEXT_STEPS item 6 called for the remaining streamed-install edge cases to
be covered in the peer-cli matrix. Add S43-S47 for already-installed
rejection, corrupt archive rollback, sender disconnect, receiver cancel,
and sorted multi-archive streaming.

The receiver-cancel scenario needs the harness to drive the same runtime
path as the GUI, so `lanspread-peer-cli` now accepts a narrow
`cancel-download` command that forwards to `PeerCommand::CancelDownload`.
A parser test covers the new JSONL command shape.

Add `fixture-multi/cnctw`, a tiny two-archive RAR fixture. S47 uses it to
prove streamed installs process root `.eti` archives in sorted order and
commit only extracted `local/` payloads, not the root archives or
`version.ini` sentinel.

Test Plan:
- just fmt
- python3 -m py_compile crates/lanspread-peer-cli/scripts/run_extended_scenarios.py
- python3 crates/lanspread-peer-cli/scripts/run_extended_scenarios.py S43 S44 S45 S46 S47 --build-image
- just test
- just clippy
- git diff --check
- git diff --cached --check

Refs: NEXT_STEPS.md item 6

crates/lanspread-peer-cli/src/main.rs

@@ -267,6 +267,13 @@ async fn handle_command(
             })?;
             Ok(json!({"queued": true, "game_id": game_id}))
         }
+        CliCommand::CancelDownload { game_id } => {
+            ensure_catalog_game(shared, game_id).await?;
+            sender.send(PeerCommand::CancelDownload {
+                id: game_id.clone(),
+            })?;
+            Ok(json!({"queued": true, "game_id": game_id}))
+        }
         CliCommand::Install { game_id } => {
             ensure_catalog_game(shared, game_id).await?;
             ensure_no_active_operation(shared, game_id).await?;