mbproxy/docs: retire superseded design/plan docs and dissolve DL260/

The standalone design.md, kpi.md, operations.md, and the docs/plan/
phase tree were point-in-time planning artefacts now superseded by the
topic-organized docs/ tree (Architecture/, Features/, Operations/,
Reference/, Testing/). The DL260/ folder mixed a device-reference doc, a
test fixture, a sample test, and a screenshot; its contents now live in
their natural homes (dl205.md + mbtcp_settings.JPG under docs/Reference/,
dl205.json next to its launcher in tests/sim/, sample test dropped).

All cross-references in the surviving docs, README, CLAUDE.md, the config
template, and source comments are repointed to the new locations.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mbproxy/tests/Mbproxy.Tests/Bcd/BcdTagMapBuilderTests.cs

@@ -148,7 +148,7 @@ public sealed class BcdTagMapBuilderTests
 
     /// <summary>
     /// Same-address entries appearing in BOTH Global AND Add are the documented
-    /// width-override pattern (design.md "Hybrid tag resolution"). They must NOT
+    /// width-override pattern (docs/Features/BcdRewriting.md "Hybrid tag resolution"). They must NOT
     /// be flagged as duplicates; Add wins.
     /// </summary>
     [Fact]

mbproxy/tests/Mbproxy.Tests/Proxy/BcdPduPipelineTests.cs

@@ -404,7 +404,7 @@ public sealed class BcdPduPipelineTests
 
     /// <summary>
     /// DL205/DL260 caps FC03/FC04 reads at qty=128 (above Modbus spec's 125; documented
-    /// in DL260/dl205.md). The proxy must NOT truncate the qty field — a request with
+    /// in docs/Reference/dl205.md). The proxy must NOT truncate the qty field — a request with
     /// qty &gt; 128 at non-BCD addresses must pass through unchanged so the PLC's own
     /// validator returns exception 03 to the client. This is the transparent-pass-through
     /// contract for FCs and addresses the rewriter doesn't own.

mbproxy/tests/Mbproxy.Tests/Proxy/Multiplexing/MultiplexerE2ETests.cs

@@ -172,7 +172,7 @@ public sealed class MultiplexerE2ETests
         int proxyPort = PickFreePort();
 
         // Configure three BCD addresses each width 16 for FC06 writes. The sim profile's
-        // writable HR range is [200..209] (see DL260/dl205.json's "write" list); reads
+        // writable HR range is [200..209] (see tests/sim/dl205.json's "write" list); reads
         // outside that range succeed but writes return exception 02. We use 200/202/204.
         var config = new Dictionary<string, string?>
         {

mbproxy/tests/Mbproxy.Tests/Proxy/Multiplexing/ReadCoalescingE2ETests.cs

@@ -207,7 +207,7 @@ public sealed class ReadCoalescingE2ETests
         await Task.Delay(300, TestContext.Current.CancellationToken);
 
         // Five different seeded addresses, sequential reads — none can coalesce.
-        // Selected from DL260/dl205.json's seeded ranges (200..209, 1024, 1040..1042).
+        // Selected from tests/sim/dl205.json's seeded ranges (200..209, 1024, 1040..1042).
         ushort[] addrs = [200, 201, 202, 203, 204];
         using (var client = new TcpClient())
         {

mbproxy/tests/Mbproxy.Tests/Sim/SimulatorSmokeTests.cs

@@ -6,7 +6,7 @@ namespace Mbproxy.Tests.Sim;
 
 /// <summary>
 /// End-to-end smoke tests that verify the pymodbus DL205 simulator is reachable and
-/// serves the expected seeded register values from <c>DL260/dl205.json</c>.
+/// serves the expected seeded register values from <c>tests/sim/dl205.json</c>.
 /// </summary>
 /// <remarks>
 /// All three tests call <see cref="Assert.Skip"/> when