fix(desktop): probe legacy Goose install dir on Windows (#3248)

Goose's pre-[#2680](https://github.com/block/buzz/pull/2680) Windows
installer unpacked the CLI to `%USERPROFILE%\goose\goose.exe`. That
directory is on no standard `PATH`, and `common_binary_paths()` never
probed it, so users who installed Goose with the legacy installer stayed
permanently undiscovered — the residual half of #2239.

`resolve_command_uncached` finds binaries outside `PATH` only by
scanning `common_binary_paths()`, so adding the directory there is the
whole fix: Windows basename expansion already supplies
`goose.exe`/`.cmd`/`.bat`, and discovery, readiness probes, and spawn
all route through the same shared resolver. No Goose-specific resolution
path is introduced. The entry sits beside the existing Codex
`%LOCALAPPDATA%\Programs\OpenAI\Codex\bin` probe in the same
`#[cfg(windows)]` block.

The regression test is `#[cfg(windows)]` and is CI-reachable, not dead
code — the `desktop-build-windows` job runs `cargo test --manifest-path
desktop/src-tauri/Cargo.toml --target $env:TARGET` on `windows-latest`.
It asserts the probe list rather than planting a binary:
`common_binary_paths` is a process-lifetime `OnceLock`, so a test cannot
deterministically re-seed `USERPROFILE`, and planting an executable
under the real user profile is not an acceptable side effect. Verified
locally by widening the `cfg` to build on macOS — the test passes with
the probe and fails without it.

The `check-file-sizes.mjs` override for `managed_agents/discovery.rs`
moves 1835 → 1841, the exact post-`cargo fmt` gate count. Verified both
directions: 1841 passes, 1840 fails.

Signed-off-by: Will Pfleger <pfleger.will@gmail.com>

desktop/scripts/check-file-sizes.mjs

@@ -344,7 +344,9 @@ const overrides = new Map([
   // absent, so AdapterMissing replaces the misleading NotInstalled. Includes
   // the deliberate-divergence doc comments; net after the inline preset
   // entries.push block collapsed into the helper.
-  ["src-tauri/src/managed_agents/discovery.rs", 1835],
+  // +6: legacy Goose Windows install dir (%USERPROFILE%\goose) probed in
+  // common_binary_paths so pre-#2680 standalone installs are discoverable.
+  ["src-tauri/src/managed_agents/discovery.rs", 1841],
   // BYOH — save_custom_harness_to_dir (backup-swap atomic write) + save_and_warm /
   // delete_and_warm (persist-mutex serialization for concurrent-safe registry
   // refresh, B-6). Also: id/collision/load/registry tests (from the file base) +