chore(spec): regenerate spec-changes.json and the upgrade guide after merging main at e75dced (step 18: 64 conversions, 326 semantic entries)

main added two step-18 semantic entries since b460153:
sys-view-definition-retired (#22374) and
try-catch-and-retry-policy-undeclared-keys-refused (#22380), and #22380
reworded the existing entry flow-builtin-node-config-undeclared-keys-refused.
At protocol 18 both generators project every step-18 entry, so both
documents gain the two entries and carry the reworded text. The conversion
ids are unchanged. registry.ts is current as merged
(check:migration-registry exits 0), so it is not regenerated.

Claude-Session: https://claude.ai/code/session_01VZqqwTj2wsihZEbfT6yyYN
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude