Add devcontainer configuration for GitHub Codespaces

[Copilot]

Enables GitHub Codespaces for debugging PRs by providing a containerized development environment with all build dependencies and debugging tools.

Configuration Files

• .devcontainer/devcontainer.json - VSCode configuration with C++ extensions (cpptools, cmake-tools, copilot), auto-initializes git submodules
• .devcontainer/Dockerfile - Ubuntu:latest base with dependencies from CI workflow
• .devcontainer/README.md - Usage documentation and build instructions

Dependencies & Tools

Build dependencies match GitHub Actions workflow:

• libssl-dev, sqlite3, libsqlite3-dev, cmake, libcurl4-openssl-dev, uuid-dev, libgtest-dev

Development tools:

• Debuggers: gdb, lldb, gdbserver
• Analysis: valgrind, clang-tidy, clang-format
• Build: ninja-build, pkg-config

Runs as non-root vscode user with sudo access.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Create devcontainer to enable CodeSpaces</issue_title>
<issue_description>Based on the GitHub Action in .github/workflows/ccpp.yml, create a dev container in the workspace (use the latest ubuntu, not ubuntu 22) with all the tools needed to build and test the library plus typical C++ development and debugging tools. I'd like to use Codespaces to debug some failing PRs.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create devcontainer to enable CodeSpaces #187

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[bbockelm]

LGTM.