docs: link release notes to GitHub instead of duplicating them

The site page had stopped at v0.9.10 while the integration shipped v1.5.0
-- around twenty releases behind, stale since early July. It was a hand
copy of RELEASENOTES.md, so it only stayed current if someone remembered
to update two files, and nobody did.

Copying the file in at build time was the obvious alternative and does
not work: RELEASENOTES.md contains links relative to the repository root,
which resolve to nothing once rendered at /release-notes/.

So the page now points at the GitHub releases, which are written as part
of cutting each release and are therefore always current. It keeps its
place in the nav, notes that HACS shows pending release notes before you
install, and explains where breaking changes appear and how to roll back.

CLAUDE.md gains the general form: prefer linking to a canonical source
over copying it. A page restating something maintained elsewhere is a
second copy kept in step by hand, and it never is.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: 0xAHA

CLAUDE.md

@@ -162,6 +162,12 @@ Before calling a change complete, ask which page would now be wrong:
 | New supported model | `hardware/models.md`, `hardware/autodetection.md` |
 | Gateway or adapter finding | `troubleshooting/rs485-gateways.md` |
 
+**Prefer linking to a canonical source over copying it.** A page that restates something
+maintained elsewhere — release notes, a register table, a version number — is a second copy
+that has to be kept in step by hand, and it never is. Link to the source, or generate the
+page from it. Only duplicate when the copy is genuinely for a different audience, and then
+add a test that holds the two together.
+
 Two things that make this fail quietly:
 
 - **A new page must be added to `mkdocs.yml` nav.** The build succeeds without it, so