feat(library): Windows Epic + GOG store providers

EpicProvider reads the launcher's local .item manifests under %ProgramData% (no auth,
launcher need not run) with Playnite's exclusion filter (skip UE_* components +
non-launchable addons + dead install dirs); cover art from the base64 catcache.bin
(public Epic CDN, best-effort). Launch via the com.epicgames.launcher:// URI opened
through explorer.exe — the namespace:catalogItemId:appName triple, with a bare-appName
fallback so a launch is never dropped.

GogProvider enumerates HKLM\SOFTWARE\WOW6432Node\GOG.com\Games (winreg) + each
goggame-<id>.info primary FileTask into a direct-exe spawn (no Galaxy, dodges its
cold-start/anti-cheat). GOG cover art (public api.gog.com) is deferred — it needs an
HTTP fetch + cache off the hot all_games() path — so GOG is title-only for now.

windows_launch_for gains epic/gog arms; both providers wired into all_games() under
cfg(windows). Deps: base64 moved to the cross-platform table (Epic catcache decode +
Lutris art encode both need it); winreg added on the Windows target. Windows unit tests
cover the Epic exclusion filter + URI builder and the GOG spawn + play-task parsing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -2752,6 +2752,7 @@ dependencies = [
  "wayland-scanner",
  "windows 0.62.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "windows-service",
+ "winreg",
  "x509-parser",
  "xkbcommon",
 ]
@@ -4946,6 +4947,16 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "winreg"
+version = "0.56.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7d6f32a0ff4a9f6f01231eb2059cc85479330739333e0e58cadf03b6af2cca10"
+dependencies = [
+ "cfg-if",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "wit-bindgen"
 version = "0.51.0"