docs(releases): draft the 17.5.0 release notes and upgrade checklist

Compile content/docs/releases/v17/17-5.mdx from the 868 changesets pending
on main at ab6fb02 (every changeset read in full, triaged into breaking /
new / fix / internal), cross-checked against the 18 ADR-0087 conversions
registered under protocol major 18 since 17.4.0. Register the page in the
v17 meta.json.

The page is a pre-cut draft: an MDX comment at its top lists the four
release-time edits (publish date, late changesets, CHANGELOG entry count,
v17/index.mdx status blockquote). v17/index.mdx is deliberately untouched
so the page claims nothing about a release that has not happened.

Claude-Session: https://claude.ai/code/session_014VGCS11YUtYAiinRcdqQwL
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude