feat(#138): Reorganise .devcontainer/ into autonomous/, scripts/, and a real VS Code devcontainer (#139)

* plan(#138): initial brief from issue

* plan(#138): review brief

* plan(#138): create task breakdown

* feat(#138): implement tasks

* feat(#138): complete implementation

Author: leecampbell-codeagent

.devcontainer/devcontainer.json

@@ -0,0 +1,19 @@
+{
+  "name": "HdrHistogram.NET",
+  "image": "mcr.microsoft.com/devcontainers/dotnet:8.0",
+  "features": {
+    "ghcr.io/devcontainers/features/node:1": {
+      "version": "20"
+    },
+    "ghcr.io/devcontainers/features/github-cli:1": {}
+  },
+  "postCreateCommand": "dotnet restore && npm install -g @anthropic-ai/claude-code",
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "ms-dotnettools.csdevkit",
+        "editorconfig.editorconfig"
+      ]
+    }
+  }
+}

CONTRIBUTING.md

@@ -51,4 +51,6 @@ dotnet test ./HdrHistogram.UnitTests/HdrHistogram.UnitTests.csproj -v q -c Relea
 - Shell scripts require LF line endings.
 - `.gitattributes` normalises line endings on checkout, so no manual intervention is needed.
 - All platforms (Windows, macOS, Linux) with the .NET 8 SDK can build and test natively with no container required.
-- `.devcontainer/` exists in the repository but contains agent-automation infrastructure only (`fleet.sh`, `agent-loop.sh`, etc.) and is not intended for human contributors.
+- `.devcontainer/` contains a VS Code / GitHub Codespaces devcontainer for human contributors.
+- `autonomous/` contains the agent Docker infrastructure (`Dockerfile`, `agent-loop.sh`, etc.) used for autonomous operation.
+- Host-side entry points for running agents are `scripts/run.sh` (single agent) and `scripts/fleet.sh` (multi-agent fleet).