Problem: members can't tell which rules their repo follows

[zolotokrylin]

Problem

Every repo in the org is governed by the Developer Guidelines, but nothing
states it and nothing shows it. There is no rule declaring that the Guidelines
apply org-wide, so the scope lives in people's heads. And a member landing in
a repo sees a README that jumps straight into local instructions, with no
statement that the repo adheres to holdex/developers and no link to the rules
it inherits.

hr-internal already depends on this scope from the other side: HR-001 inherits
the Guidelines by reference and adds only its private layer on top. That
inheritance has no counterpart here to point at.

Solution

1. Add DEV-001, a foundation rule declaring that the Developer Guidelines apply
   to every repo in the org, that no repo restates or overrides them, and that
   repo-local rules may only add what the Guidelines deliberately exclude. It
   sits above the category scheme rather than inside DEV-0xx Authoring.
2. Amend DEV-338 to require the root README to open with a statement that the
   repo adheres to the Developer Guidelines, linking holdex/developers. Define
   the exact opener so it is copy-pasteable, and add it to the acceptance
   criteria.