fix(claude-dev, mistral-dev): persist credentials via a named volume, fixing GitHub Codespaces

[baxyz]

Summary

Fixes #66. GitHub Codespaces doesn't support host bind-mounts at all — confirmed in VS Code's docs. ${localEnv:HOME} can resolve to an empty string there, turning claude-dev's ${localEnv:HOME}/.claude mount source into the literal path /.claude, which doesn't exist, failing the whole codespace build. mistral-dev has the same mount shape and hits the same failure.

Fix

Switched both features from a host bind-mount to a Docker named volume, scoped by ${localEnv:USER} (e.g. helpers4-claude-credentials-${localEnv:USER}):

• Docker creates a missing volume automatically, so there's no crash risk on Codespaces, and no initializeCommand is needed anymore.
• Scoping by ${localEnv:USER} rather than ${devcontainerId} (the pattern pnpm-store/playwright-dev use) keeps credentials shared across every local devcontainer for the same OS user — matching the old bind-mount's behavior — instead of isolating per project like a cache would.

install.sh and the generated setup-credentials.sh needed no changes — they only check whether /mnt/h4claude//mnt/h4vibe is a mounted directory, not how.

Bumped claude-dev to 1.0.6 and mistral-dev to 1.0.4, and documented the new ${localEnv:USER}-scoped volume pattern in AGENTS.md alongside the existing ${devcontainerId} one.

Test plan

• Both devcontainer-feature.json files are valid JSON
• install.sh/setup-credentials.sh confirmed mount-type-agnostic (only checks [ -d "$STAGED" ])
• No automated regression coverage possible — this is Codespaces-specific runtime behavior the existing devcontainer features test matrix (local Docker, plain Linux GH Actions runners) can't reproduce

🤖 Generated with Claude Code

[github-actions]

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📋 Pipeline Status

	Job	Status
✅	🧾 Conventional Commits	passing
✅	🔖 Version Bump	passing
✅	🧪 Feature Tests	passing
✅	🐚 ShellCheck	passing

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_{🤖 Generated by @helpers4 CI • 2026-08-30}