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

IMPL_DECISIONS.md

@@ -32,5 +32,5 @@
   rendering follows backend state instead of reverse-engineering it from
   `installed && !downloaded`.
 - Removed Tauri's parallel whole-library filesystem scan. The UI database keeps
-  bundled catalog metadata, while peer `LocalGamesUpdated` snapshots now own
+  bundled catalog metadata, while peer `LocalLibraryChanged` snapshots now own
   `downloaded`, `installed`, `local_version`, and `availability`.