feat(tauri): add unpack logs viewer for unrar attempts

Captures stdout, stderr, exit status and start/finish timestamps for every
unrar sidecar invocation and exposes them through a dedicated "Unpack Logs"
window. Triggered by the need to debug why a particular game's archive
failed to extract -- previously the only artifact of a failed unpack was a
log line in the Tauri process stdout, which is awkward to inspect on an
end-user machine.

Implementation:

* `LanSpreadState` gains an in-memory ring buffer (`unpack_logs`) capped at
  `MAX_UNPACK_LOGS` (100). The previous monolithic `do_unrar` is split into
  `prepare_unrar_paths` and `run_unrar_sidecar` so every failure path (mkdir
  failure, canonicalize failure, non-UTF-8 destination, sidecar spawn error,
  non-zero exit) records an `UnpackLogEntry` before bailing.
* A `get_unpack_logs` Tauri command returns the current snapshot; an
  `unpack-logs-updated` event is emitted after every write so the viewer can
  refresh without polling.
* The React `App` component now routes on `?view=unpack-logs` and renders a
  dedicated `UnpackLogsWindow`. The main window opens the viewer via
  `WebviewWindow` with label `unpack-logs`; an existing window is focused
  instead of being recreated.

Capability scoping: the new window is given its own capability file
(`capabilities/unpack-logs.json`) granting only `core:default`. The main
capability is unchanged in window scope and only gains the two permissions
the main window itself needs (`core:window:allow-set-focus` to focus an
existing log window, `core:webview:allow-create-webview-window` to spawn
it). Splitting the capability keeps the log window from inheriting
`shell:allow-open`, `dialog:default` and `store:default`, which it has no
reason to use.

Known limitations (intentionally out of scope here):

* Logs are process-local; they vanish on app restart. Persistence can be
  added later if it turns out users want to inspect failures across runs.
* Entries are presented as a flat chronological list identified by archive
  path. No per-game grouping or filtering yet -- the archive filename is
  usually enough to identify the game in practice.
* The `unpack-logs-updated` event carries no payload; the viewer re-fetches
  the full snapshot on every notification. Acceptable given the 100-entry
  cap, but a payload-bearing event would be cheaper if the cap grows.

Test plan:

* `just clippy` and `just build` are clean.
* Manual: start the GUI, point it at a games directory containing at least
  one peer-hosted game, trigger an install, then click "Unpack Logs". The
  window should show one entry per unrar invocation with stdout, stderr,
  status code and timestamps; stderr/error lines render in the warning
  color. Triggering further unpacks should update the open window live via
  the `unpack-logs-updated` event without manual refresh.
* Negative path: rename or remove the archive between handshake and
  extraction to force a canonicalize failure; confirm a failed entry with
  the corresponding stderr appears in the viewer.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/lanspread-tauri-deno-ts/src-tauri/capabilities/default.json

@@ -7,8 +7,10 @@
   ],
   "permissions": [
     "core:default",
+    "core:window:allow-set-focus",
+    "core:webview:allow-create-webview-window",
     "shell:allow-open",
     "dialog:default",
     "store:default"
   ]
-}
+}