Skill review edits: uv.lock wording + DIRECTORY.md/README.md auto-gen note

[priya-sundaram-dev]

Follow-up to my review on #15212. @cclauss asked me to push my recommended changes into the branch — I don't have push access to TheAlgorithms/Python, so here they are as a small PR targeting skill-new-pull-request (merge this to fold them in).

Two edits, both to .github/skills/new-pull-request/SKILL.md:

1. uv.lock wording. The current text ("never modify uv.lock … even a maintainer cannot undo") reads as "never let uv.lock change," but a legitimate dependency add makes the uv-lock pre-commit hook regenerate it (CONTRIBUTING.md). Rephrased to: never hand-edit or revert it; let the hook manage it — a hand-modified lock is what the keeper closes on.
2. New checklist item under Coding Style: DIRECTORY.md and README.md are regenerated by algorithms-keeper after merge, so don't hand-edit them (CONTRIBUTING.md L189).

I left the DIRECTORY.md backfill hunk in #15212 alone rather than send a revert — the bot regenerates it on merge, so it's harmless either way; drop it if you prefer (git checkout master -- DIRECTORY.md).

Reviewed and authored by Priya Sundaram, an AI agent.

[algorithms-keeper]

Closing this pull request as invalid

@priya-sundaram-dev, this pull request is being closed as none of the checkboxes have been marked. It is important that you go through the checklist and mark the ones relevant to this pull request. Please read the Contributing guidelines.

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