refactor: prune unconsumed peer lifecycle events

An emit-vs-listen audit of the event surface showed the GUI is
state-as-source-of-truth: useGames renders the complete `games-list`
snapshot (full library + active_operations) and reconstructs status from
it, not from a stream of granular events. Several PeerEvents were emitted
but had no consumer at all -- no frontend `listen()` and no peer-cli
scenario assertion -- so they were pure dead weight that made the backend
look event-driven when it no longer is.

This prunes that dead surface in two parts.

1. Remove three PeerEvent variants with no consumer: InstallGameBegin,
   UninstallGameBegin, and RemoveDownloadedGameBegin. The operation-start
   transition is still observable via ActiveOperationsChanged (the
   snapshot already carries the Installing/Updating/Uninstalling/
   RemovingDownload kind), so nothing is lost. This drops their emit
   sites in handlers.rs, the begin-event assertions in the peer's
   lifecycle unit tests (the asserted sequence is now
   ActiveOperationsChanged(kind) -> LocalLibraryChanged ->
   ActiveOperationsChanged([]) -> *Finished), the peer-cli JSONL
   mappings (install-begin/uninstall-begin/remove-download-begin) plus
   the now-orphaned install_operation_name helper and InstallOperation
   import, and the matching Tauri handler arms.

2. Drop Tauri webview emits that no frontend listener consumed:
   peer-local-ready, game-download-begin, game-download-pre,
   game-download-finished, game-uninstall-finished, and
   peer-connected/-disconnected/-discovered/-lost. The log lines and all
   real side effects are kept (handle_got_game_files still forwards
   PeerCommand::DownloadGameFiles). The orphaned emit_peer_addr_event and
   handle_download_finished helpers and the now-unused SocketAddr import
   are removed. peer-runtime-failed is kept pending a decision on
   surfacing runtime failures in the GUI.

Why not re-wire instead: under state-as-source-of-truth, per-event UI
state is exactly the pattern this project abandoned. Live progress
already flows via game-download-progress, and the peer-cli's chunk,
timing-trigger, and transition assertions read events that are retained
(download-begin, download-chunk-finished, the *-finished/*-failed
terminals), so test coverage is unchanged.

Behavior change: none functional. The Tauri backend no longer emits
events nothing listened to; the GUI is unchanged. The peer-cli no longer
emits the three *-begin JSONL events. PeerEvent is a workspace-internal
UI-reporting type, not a wire-protocol type, so there is no protocol or
version impact and all consumers are updated in this commit.

Docs: PEER_CLI_SCENARIOS.md S39 no longer lists install-begin (with a
note that the start transition is visible via active-operations-changed),
and a dated Run Log entry records the removal. The historical 2026-05-18
run-log note is left intact as a dated observation.

Test Plan:
- just test: pass (incl. peer lifecycle event-sequence tests).
- just clippy: pass (-D warnings, all targets).
- just frontend-test: pass (11/11, incl. streamed-install gating/labels).
- just build: pass (release, no bundle).
- Not run: the Docker S39-S47 matrix (run_extended_scenarios.py); those
  scenarios never asserted the removed *-begin events, so coverage is
  unaffected. just fmt's tombi step needs network and was skipped; no
  TOML changed.

Refs: peer event-surface emit-vs-listen audit; no external consumers of
the removed events.

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

@@ -17,7 +17,6 @@ use lanspread_peer::{
     ActiveOperation,
     ActiveOperationKind,
     ExternalUnrarStreamProvider,
-    InstallOperation,
     NoopStreamInstallProvider,
     OutboundTransfers,
     PeerCommand,
@@ -541,16 +540,10 @@ async fn update_state_from_event(shared: &SharedState, event: PeerEvent) -> (&'s
             download_terminal_event(shared, "download-failed", id).await
         }
         PeerEvent::DownloadGameFilesAllPeersGone { id } => game_id_event("download-peers-gone", id),
-        PeerEvent::InstallGameBegin { id, operation } => (
-            "install-begin",
-            json!({"game_id": id, "operation": install_operation_name(operation)}),
-        ),
         PeerEvent::InstallGameFinished { id } => game_id_event("install-finished", id),
         PeerEvent::InstallGameFailed { id } => game_id_event("install-failed", id),
-        PeerEvent::UninstallGameBegin { id } => game_id_event("uninstall-begin", id),
         PeerEvent::UninstallGameFinished { id } => game_id_event("uninstall-finished", id),
         PeerEvent::UninstallGameFailed { id } => game_id_event("uninstall-failed", id),
-        PeerEvent::RemoveDownloadedGameBegin { id } => game_id_event("remove-download-begin", id),
         PeerEvent::RemoveDownloadedGameFinished { id } => {
             game_id_event("remove-download-finished", id)
         }
@@ -686,10 +679,6 @@ fn active_operation_name(operation: ActiveOperationKind) -> &'static str {
     (&operation).into()
 }
 
-fn install_operation_name(operation: InstallOperation) -> &'static str {
-    (&operation).into()
-}
-
 fn runtime_component_name(component: PeerRuntimeComponent) -> &'static str {
     (&component).into()
 }