docs: link the run page to locking and syncing

[monsonego]

Summary

• link the project uv run concept page to the locking and syncing page
• point readers to the projects guide for a task-oriented overview of uv run

Problem

The "Running commands" concept page explains that uv run keeps the environment up to date, but it does not point readers to the documentation that explains that locking and syncing behavior in more detail.

Changes

• add a short follow-up sentence after the automatic sync explanation in docs/concepts/projects/run.md
• link to the locking and syncing concept page and the projects guide section for uv run

Validation

• git diff --check

Closes #15407

[zanieb]

This should probably be in an admonition?

[monsonego]

Good call. I've updated it to a note admonition in e5ec847 so it matches the surrounding docs style.