CrossRelay stage 0+1: Go gateway with Anthropic<->Chat Completions relay, Tauri shell, bilingual management UI

- Go gateway (stdlib only): /v1/messages non-stream + SSE, /v1/messages/count_tokens,
  management API /api/* (providers CRUD, apply/restore, settings, backups, logs)
- Protocol conversion: Anthropic Messages <-> Chat Completions with a streaming
  state machine keyed by content block index (text, tool_use, parallel calls)
- ~/.claude/settings.json guarded read/write: timestamped backups, managed env
  keys only, one-click restore
- Tauri 2 shell: spawns the gateway sidecar, parses the random port from stdout,
  stdin pipe watchdog prevents orphans, kills the child on exit
- React frontend: Dashboard/Providers/Settings, zh-CN + en-US, TanStack Query
- Tests: Go table-driven + httptest integration (all green), vitest + RTL

scripts/build-gateway.ps1

@@ -0,0 +1,25 @@
+# Builds the CrossRelay gateway binary into bin/.
+# Usage: powershell -File scripts/build-gateway.ps1 [-GOOS windows|darwin|linux] [-GOARCH amd64|arm64]
+param(
+	[string]$GOOS = "windows",
+	[string]$GOARCH = "amd64"
+)
+
+$ErrorActionPreference = "Stop"
+
+$repoRoot = Split-Path -Parent $PSScriptRoot
+$binDir = Join-Path $repoRoot "bin"
+New-Item -ItemType Directory -Force -Path $binDir | Out-Null
+
+$exe = if ($GOOS -eq "windows") { "gateway.exe" } else { "gateway" }
+$out = Join-Path $binDir "$GOOS-$GOARCH-$exe"
+
+$env:GOOS = $GOOS
+$env:GOARCH = $GOARCH
+go build -o $out ./cmd/gateway
+
+# Keep a stable name for the current platform so the Tauri app finds it.
+$stable = Join-Path $binDir $exe
+Copy-Item $out $stable -Force
+
+Write-Host "built $out (also $stable)"