feat(#48): make one config work for both development and deployment

The repo already layered file defaults under environment overrides, on
both the backend (settings.yml < GOAUTO_*) and the frontend
(.env.production < process.env). What was missing was a translator for
production: config.yaml only ever existed for the PowerShell launchers,
so a packaged binary read none of it and had no database credentials
either — SYB was inheriting an existing gap, not creating one.

The server now reads config.yaml itself, between settings.yml and the
environment. Lookup is GOAUTO_CONFIG, then ./config.yaml, then beside the
executable, so a packaged binary works wherever it is started. An absent
file is not an error: containers supply everything through the
environment. Scalars are read by YAML type and coerced, so an unquoted
all-digit password cannot take startup down over a quoting detail.

This removed the need for a Read-SybConfig in PowerShell: the launcher
just hands over the path it already knows, rather than reimplementing a
YAML parser.

The server also serves the built frontend when dist is present, which is
what .env.production's empty VUE_APP_BASE_API already assumes. The
history fallback is restricted to non-API GETs, and is not installed at
all without dist, so development 404s stay 404s.

Precedence is mutation-tested: applying the local file after the
environment instead of before makes the layering test fail.

Not verified: the PowerShell change and any Windows deployment — both
need a run on the Windows side.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/start-server.ps1

@@ -196,6 +196,9 @@ try {
         Remove-Item Env:MYSQL_PWD -ErrorAction SilentlyContinue
     }
 
+    # 让服务端自己读同一个 config.yaml，取出 syb 凭据等本地配置。
+    # 下面的 GOAUTO_* 变量优先级高于文件，所以数据库和端口仍以脚本算出的为准。
+    $env:GOAUTO_CONFIG = $ConfigPath
     $env:GOAUTO_DB_DRIVER = "mysql"
     $env:GOAUTO_DB_DSN = "${DatabaseUser}:${plainPassword}@tcp(${DatabaseHost}:${DatabasePort})/${DatabaseName}?charset=utf8mb4&parseTime=True&loc=Local&timeout=5s"
     $env:GOAUTO_SERVER_PORT = [string]$portConfig.Server
@@ -242,5 +245,6 @@ finally {
     Remove-Item Env:GOAUTO_DB_DSN -ErrorAction SilentlyContinue
     Remove-Item Env:GOAUTO_DB_DRIVER -ErrorAction SilentlyContinue
     Remove-Item Env:GOAUTO_SERVER_PORT -ErrorAction SilentlyContinue
+    Remove-Item Env:GOAUTO_CONFIG -ErrorAction SilentlyContinue
     $plainPassword = $null
 }