refactor(peer): split local library and operation UI events

Replace the `a9f9845` local-update dedup cache with explicit peer event
semantics. Local scans now emit `LocalLibraryChanged` when the library changes,
while operation mutations emit `ActiveOperationsChanged` from the mutation
path. Tauri keeps joining those facts into the existing `games-list-updated`
payload, so the frontend contract stays stable.

This removes the cache/invalidation coupling between scan emission and
operation state. The remaining forced local snapshot is explicit: accepted game
directory changes can refresh the UI for an equivalent new path without sending
a peer library delta.

Operation guard cleanup and liveness cancellation now publish the same active
operation snapshot as normal command-handler transitions. The peer CLI JSONL
events follow the same split with `local-library-changed` and
`active-operations-changed`.

Test Plan:
- `just fmt`
- `CARGO_BUILD_RUSTC_WRAPPER= just test`
- `CARGO_BUILD_RUSTC_WRAPPER= just clippy`
- `git diff --check`

Refs: CLEAN_CODE_PLAN_1.md

crates/lanspread-peer/README.md

@@ -37,7 +37,8 @@ lifetime of the process:
    to keep peer liveness up to date and prunes stale entries from `PeerGameDB`.
 4. **Local game monitor** (`run_local_game_monitor`) – watches the configured
    game directory and each game root non-recursively, gates per-ID rescans while
-   operations are active, and runs a 300-second fallback scan for missed events.
+   operations are active, emits local-library changes separately from active
+   operation snapshots, and runs a 300-second fallback scan for missed events.
 
 `scan_local_library` maintains a lightweight on-disk index and produces both a
 `GameDB` and protocol summaries. A game is downloaded only when its root-level