test(peer-cli): cover full docker scenario matrix

Merge the S18-S36 scenario ideas into the official peer-cli scenario matrix
and add a Docker-backed runner that now exercises S1-S36 with concrete file
proofs. The runner creates temporary fixtures under .lanspread-peer-cli, drives
JSONL peer containers, checks transferred roots with diff and SHA-256 manifests,
and covers startup, discovery, transfer, failure, mutation, concurrency, mesh,
lifecycle, and catalog edge cases.

The scenarios exposed a few harness/runtime boundary gaps that would otherwise
make the contract ambiguous. The peer CLI now rejects self-connects, rejects
commands for game IDs outside the receiver catalog, filters unknown remote games
from its command/event surface, and reports duplicate active same-game commands
as operation-in-progress errors. The peer core also refuses non-catalog download
commands before transfer, and PeerGameDB has a unit check that address changes
preserve identity and library state.

S12 and S28 remain unit-level invariants because the CLI cannot stably race raw
serve-gate requests or rebind a live listener without restart. The runner treats
those scenarios as covered by just test and checks the expected unit test names
appear in the output.

Test Plan:
- just fmt
- python3 -m py_compile crates/lanspread-peer-cli/scripts/run_extended_scenarios.py
- RUSTC_WRAPPER= just test
- RUSTC_WRAPPER= just clippy
- RUSTC_WRAPPER= just peer-cli-build
- just peer-cli-image
- python3 crates/lanspread-peer-cli/scripts/run_extended_scenarios.py
- git diff --check

Refs: PEER_CLI_SCENARIOS.md S1-S36

crates/lanspread-peer/src/handlers.rs

@@ -198,6 +198,14 @@ pub async fn handle_download_game_files_command(
     install_after_download: bool,
 ) {
     log::info!("Got PeerCommand::DownloadGameFiles");
+    if !catalog_contains(ctx, &id).await {
+        log::warn!("Ignoring download command for non-catalog game {id}");
+        if let Err(send_err) = tx_notify_ui.send(PeerEvent::DownloadGameFilesFailed { id }) {
+            log::error!("Failed to send DownloadGameFilesFailed event: {send_err}");
+        }
+        return;
+    }
+
     let games_folder = { ctx.game_dir.read().await.clone() };
 
     // Use majority validation to get trusted file descriptions and peer whitelist