refactor: move buildable .NET source into src/, update CI/doc paths

Groups the repo root into src (buildable source), docs (already existed),
and everything else (db/, scripts/, tests/, deploy/ - deployment/ops/test
assets that aren't compiled, already organized as their own folders). CI
now only needs src/ to build: dotnet restore/build/test/publish all point
at src/TaxBaik.sln, src/TaxBaik.Web/, src/TaxBaik.Proxy/.

- git mv every project (Domain, Infrastructure, Application,
  Application.Tests, Web, Web.Client, Proxy) and TaxBaik.sln into src/ as a
  unit, so relative ProjectReference/.sln paths stay valid unchanged.
- .gitea/workflows/deploy.yml: 6 dotnet restore/clean/build/test/publish
  invocations now point at src/. db/migrations and scripts/ stay at root
  (deploy_gb.sh and browser-e2e.yml only touch published output and the
  deployed URL, not source paths - verified, no changes needed there).
- scripts/validate_admin_render.sh: admin render-mode file paths now
  src/TaxBaik.Web.Client/...
- scripts/validate_kst_timestamps.sh: dropped deploy.sh from its target
  list - that script was removed in the prior cleanup commit (dead, no
  CI workflow referenced it) but this validator still expected it to exist.
- CLAUDE.md, docs/ENGINEERING_HARNESS.md, docs/ADMIN_PATTERN_CRITIQUE_WBS.md:
  updated project-structure diagram, dotnet run/build commands, and grep
  targets to the new src/ paths (also fixed a pre-existing stale path in
  ADMIN_PATTERN_CRITIQUE_WBS.md that still said TaxBaik.Web/Components/Admin
  from before that ever moved to TaxBaik.Web.Client).
- Added a Repo Root harness rule + Architecture Guardrail entries: new files
  belong under src/docs/tests/scripts/db/deploy, not loose at root; temp
  work stays outside the repo (or under a gitignored .scratch/) and is
  never committed.

Verified locally: dotnet build/test src/TaxBaik.sln (26/26 tests), and all
three scripts/validate_*.sh pass against the new layout.

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

src/TaxBaik.Proxy/Program.cs

@@ -0,0 +1,93 @@
+using System;
+using System.IO;
+using System.Net;
+using System.Net.Sockets;
+using System.Threading;
+using System.Threading.Tasks;
+
+class Program
+{
+    private const string PortFile = "/home/kjh2064/taxbaik_port";
+    private static int _fallbackPort = 5003;
+
+    static async Task Main(string[] args)
+    {
+        // Allow setting fallback port via args
+        if (args.Length > 0 && int.TryParse(args[0], out var port))
+        {
+            _fallbackPort = port;
+        }
+
+        var listener = new TcpListener(IPAddress.Loopback, 5001);
+        listener.Start();
+        Console.WriteLine($"[TaxBaik Proxy] Listening on 127.0.0.1:5001 (Forwarding to target in {PortFile})");
+
+        while (true)
+        {
+            try
+            {
+                var client = await listener.AcceptTcpClientAsync();
+                _ = HandleClientAsync(client);
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"[TaxBaik Proxy] Accept error: {ex.Message}");
+                await Task.Delay(100);
+            }
+        }
+    }
+
+    private static int GetTargetPort()
+    {
+        try
+        {
+            if (File.Exists(PortFile))
+            {
+                var content = File.ReadAllText(PortFile).Trim();
+                if (int.TryParse(content, out var port) && port > 1024 && port < 65535)
+                {
+                    return port;
+                }
+            }
+        }
+        catch { }
+        return _fallbackPort;
+    }
+
+    private static async Task HandleClientAsync(TcpClient client)
+    {
+        client.NoDelay = true;
+        int targetPort = GetTargetPort();
+        using var backend = new TcpClient();
+        backend.NoDelay = true;
+
+        try
+        {
+            using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+            await backend.ConnectAsync(IPAddress.Loopback, targetPort, cts.Token);
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"[TaxBaik Proxy] Failed to connect to backend on port {targetPort}: {ex.Message}");
+            client.Close();
+            return;
+        }
+
+        try
+        {
+            using var clientStream = client.GetStream();
+            using var backendStream = backend.GetStream();
+
+            var toBackend = clientStream.CopyToAsync(backendStream);
+            var toClient = backendStream.CopyToAsync(clientStream);
+
+            await Task.WhenAny(toBackend, toClient);
+        }
+        catch { }
+        finally
+        {
+            client.Close();
+            backend.Close();
+        }
+    }
+}

src/TaxBaik.Proxy/TaxBaik.Proxy.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>