Add build and run scripts; drop the broken Avalonia.Diagnostics reference

A wrapper around `dotnet build` earns nothing, so build.ps1/build.sh are the
full local gate instead — tool restore, package restore, format check, build,
test — in the order that fails cheapest first, with a non-zero exit on failure.
run.ps1/run.sh default to Debug and pass extra arguments through to the app.
Both flavours ship because the Desktop head targets Windows, Linux and macOS.

Writing them immediately paid for itself: the very first run failed restore on
Avalonia.Diagnostics 12.1.1, which does not exist — the package stops at 11.3.x
because Avalonia 12 moved the inspector into a separate tool with its own
installation. The reference had survived because it sat behind
Condition="'$(Configuration)' == 'Debug'", and `dotnet restore` evaluates with
the default configuration while every build so far had passed -c Release. So
`dotnet build -c Release` worked and a bare `dotnet restore` did not.

Reference removed rather than replaced: AvaloniaUI.DiagnosticsSupport pulls in a
separately installed tool, which is not a dependency to add to a skeleton without
asking. README and CLAUDE.md no longer promise F12, and both traps are written
down where the next person will hit them.

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

build.ps1

@@ -0,0 +1,97 @@
+#!/usr/bin/env pwsh
+<#
+.SYNOPSIS
+    Полный локальный гейт: формат, сборка, тесты.
+
+.DESCRIPTION
+    То, что имеет смысл прогнать перед коммитом. Обёртка вокруг `dotnet build` сама по себе
+    бесполезна — ценность здесь в том, что шаги идут в правильном порядке, падают быстро и
+    возвращают ненулевой код возврата.
+
+.PARAMETER Configuration
+    Debug или Release. По умолчанию Release — гейт должен проверять то, что уедет.
+
+.PARAMETER Fix
+    Переформатировать код вместо проверки. Без этого флага несформатированный код валит сборку.
+
+.PARAMETER SkipFormat
+    Пропустить проверку форматирования.
+
+.PARAMETER SkipTests
+    Только собрать, не запускать тесты.
+
+.EXAMPLE
+    ./build.ps1
+    Формат, сборка и тесты в Release.
+
+.EXAMPLE
+    ./build.ps1 -Fix
+    Переформатировать код, затем собрать и прогнать тесты.
+#>
+[CmdletBinding()]
+param(
+    [ValidateSet('Debug', 'Release')]
+    [string] $Configuration = 'Release',
+
+    [switch] $Fix,
+    [switch] $SkipFormat,
+    [switch] $SkipTests
+)
+
+$ErrorActionPreference = 'Stop'
+Set-Location $PSScriptRoot
+
+$solution = 'AvParser.slnx'
+$started = Get-Date
+
+function Invoke-Step {
+    param(
+        [Parameter(Mandatory)] [string] $Name,
+        [Parameter(Mandatory)] [scriptblock] $Action
+    )
+
+    Write-Host ''
+    Write-Host "==> $Name" -ForegroundColor Cyan
+
+    & $Action
+
+    # Native executables do not raise terminating errors, so the exit code is the only signal.
+    if ($LASTEXITCODE -ne 0) {
+        throw "$Name — код возврата $LASTEXITCODE"
+    }
+}
+
+try {
+    Invoke-Step 'Локальные инструменты' { dotnet tool restore }
+
+    Invoke-Step 'Восстановление пакетов' { dotnet restore $solution }
+
+    if (-not $SkipFormat) {
+        if ($Fix) {
+            Invoke-Step 'Форматирование (csharpier format)' { dotnet csharpier format . }
+        }
+        else {
+            # Before the build: an unformatted file is the cheapest possible failure.
+            Invoke-Step 'Проверка форматирования (csharpier check)' { dotnet csharpier check . }
+        }
+    }
+
+    Invoke-Step "Сборка ($Configuration)" {
+        dotnet build $solution -c $Configuration --no-restore --nologo
+    }
+
+    if (-not $SkipTests) {
+        Invoke-Step 'Тесты' {
+            dotnet test $solution -c $Configuration --no-build --nologo
+        }
+    }
+
+    $elapsed = (Get-Date) - $started
+    Write-Host ''
+    Write-Host ("OK — {0:mm\:ss}" -f $elapsed) -ForegroundColor Green
+}
+catch {
+    Write-Host ''
+    Write-Host "СБОЙ: $_" -ForegroundColor Red
+    exit 1
+}