improve PEER_AUTH_PLAN.md and re-organize files

IMPL_DECISIONS.md

@@ -1,37 +0,0 @@
-# Implementation Decisions
-
-- Added a `just test` recipe so unit tests can be run through the repository's
-  required `just ...` command surface instead of invoking `cargo test`
-  directly.
-- Renamed the frontend success event to `game-install-finished`; the old
-  unpack name no longer matched the transactional install/update lifecycle.
-- Implemented watcher rescans by reusing the app-state
-  `local_library/index.json` cache and updating a single game entry in that
-  index. This satisfies the per-ID optimized rescan requirement without adding a
-  second cache format.
-- Split full startup recovery from ordinary settled refreshes. Startup and real
-  `SetGameDir` changes run recovery plus a scan; install/update/uninstall
-  completion only rescans the affected game after operation tracking has been
-  cleared.
-- Rejected path-changing `SetGameDir` while operations are active. Same-path
-  refreshes are allowed and deliberately skip full recovery so they cannot sweep
-  download transients for in-flight work.
-- Kept a separate `active_downloads` cancellation-token map next to the single
-  `active_operations` table. The operation table is the authoritative state for
-  gates; the token map is only cancellation plumbing for in-flight downloads.
-- Treated a downloaded-but-not-installed game as immediately installable from
-  Tauri by sending `PeerCommand::InstallGame` directly. A not-downloaded game
-  still uses `GetGame`, and the peer auto-installs after the sentinel commit.
-- Removed the dead internal `PeerCommand::UpdateGame` path. The UI update button
-  now sends `FetchLatestFromPeers`, which skips local manifest serving and asks
-  latest-version peers for fresh file metadata before the normal download and
-  update transaction runs.
-- Removed the unreachable `Availability::Downloading` protocol value. Active
-  operations are reported separately, and local summaries emit only settled
-  availability.
-- Threaded availability through the UI-facing `Game` payload so `LocalOnly`
-  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 `LocalLibraryChanged` snapshots now own
-  `downloaded`, `installed`, `local_version`, and `availability`.