build: extract strings sync script for local use

[protyposis]

Extract the strings sync script for local use to scripts/sync-strings. This can be used to tidy up a PR locally and simplifies external PRs where the action-based updates cannot be pushed (see, e.g., #1363 (review)).

Also adds a task for VSCode/devcontainer.

[basnijholt]

Sorry it took me so long to get to this. I've been a bit overwhelmed by the number of AI-assisted PRs opened here recently, and I've also been spending nearly every spare hour on my biggest project so far, MindRoom.

I'm very supportive of using AI for coding, but many of these PRs still need careful human review because even plausible-looking changes can introduce subtle breakage. That backlog made me postpone reviewing them for a while.

I've now done a batch review with Codex / GPT-5.5 (xhigh). This comment is AI-assisted, but I've reviewed the concern before posting it.

This branch is stale against current main and would break the newer generated-content helper if merged as-is.

The PR moves .github/update-services.py and .github/update-strings.py into scripts/, but current main now has scripts/update-generated-content still invoking the old .github/... paths. After merging/rebasing this PR, that helper would point at files that no longer exist.

Could you rebase this and update scripts/update-generated-content to call the new paths, or delegate to the new scripts/sync-strings helper?