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>

run.ps1

@@ -0,0 +1,50 @@
+#!/usr/bin/env pwsh
+<#
+.SYNOPSIS
+    Запускает desktop-приложение.
+
+.DESCRIPTION
+    По умолчанию Debug: быстрее собирается и даёт осмысленные стеки. Инспектора в Avalonia 12
+    из коробки нет — см. README.
+
+.PARAMETER Configuration
+    Debug или Release. По умолчанию Debug.
+
+.PARAMETER NoBuild
+    Не пересобирать — запустить то, что уже собрано.
+
+.PARAMETER AppArgs
+    Всё остальное уходит в приложение как аргументы командной строки.
+
+.EXAMPLE
+    ./run.ps1
+
+.EXAMPLE
+    ./run.ps1 -Configuration Release -NoBuild
+#>
+[CmdletBinding()]
+param(
+    [ValidateSet('Debug', 'Release')]
+    [string] $Configuration = 'Debug',
+
+    [switch] $NoBuild,
+
+    [Parameter(ValueFromRemainingArguments = $true)]
+    [string[]] $AppArgs = @()
+)
+
+$ErrorActionPreference = 'Stop'
+Set-Location $PSScriptRoot
+
+$arguments = @('run', '--project', 'src/AvParser.Desktop', '-c', $Configuration)
+if ($NoBuild) {
+    $arguments += '--no-build'
+}
+if ($AppArgs.Count -gt 0) {
+    $arguments += '--'
+    $arguments += $AppArgs
+}
+
+Write-Host "==> dotnet $($arguments -join ' ')" -ForegroundColor Cyan
+& dotnet @arguments
+exit $LASTEXITCODE