feat: install gh CLI and disable debuginfod

[gabrielfrasantos]

Problem

Two quality-of-life gaps affect every project using this devcontainer:

1. gh is missing — the GitHub CLI is not installed, so any workflow that uses gh (issue/PR creation, release management, etc.) requires manual installation after container creation.

2. GDB 17.1 stalls on startup — newer GDB versions have debuginfod enabled by default. Without a DEBUGINFOD_URLS override they attempt to reach external servers on every debug session, causing multi-second hangs and noisy warnings when no internet path exists to the configured endpoints.

Proposed fix

Install gh from the official CLI apt repository

The Ubuntu universe package (2.46.0-4) is stale. The official GitHub apt source ships the current release (2.97.0 as of this writing) and tracks upstream:

RUN curl -fsSL https://cli.github.com/packages/githubcli-archive-keyring.gpg \
      | dd of=/usr/share/keyrings/githubcli-archive-keyring.gpg \
 && echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/githubcli-archive-keyring.gpg] https://cli.github.com/packages stable main" \
      > /etc/apt/sources.list.d/github-cli.list \
 && apt-get update \
 && apt-get install -y gh

Set DEBUGINFOD_URLS to empty

In devcontainer.json containerEnv:

"DEBUGINFOD_URLS": ""

This is the documented, environment-level way to disable debuginfod queries — it applies to GDB launched from the terminal, from VSCode, and from any script, with no per-launch-config changes required.