Rewrite post title and excerpt on update in publish-post

[jasperf]

Stacked on #211 — base is fix/publish-post-wp-slash, so review that one first. Retarget to main once it merges.

Follows up the note at the end of #210.

Problem

publish-post --update wrote only post_content. Everything else on the update path came from the draft header and was rewritten on every run — SEO meta title, meta description, tags, category, featured image — but the post's own post_title and post_excerpt were not.

The result is incoherent rather than merely incomplete: a title corrected in the draft stays stale on the post while _genesis_title, derived from that same header, is updated to the corrected version. On one post a "WooComerce" typo survived an update that changed everything else, which is what surfaced this.

Change

The update path now writes post_title and post_excerpt alongside the body. The draft header is authoritative for both.

This is a behavior change, hence the minor bump to 5.17.0 rather than a patch. Anyone relying on the post title surviving an update will find it no longer does.

Deliberately not changed

• post_name — rewriting a slug silently breaks the live URL and needs a redirect that this tool has no business creating. When the draft's slug differs from the stored one, publish-post now warns and leaves it alone, so the drift is visible without acting on it.
• post_status — an update must not flip a draft live. --status remains create-only.

Both are commented in place so the omission reads as a decision rather than the same oversight repeating.

Verification

• bash -n passes; the shell worker was regenerated with UPDATE_ID set and a \"-containing title, then linted with php -l under PHP 8.5 — valid, with the new warning and both fields correctly escaped through the heredoc
• The new WARN: line follows the existing convention in the script and is picked up by the established grep -E '^(WARN|ABORT|ERROR):' handler, so it prints through print_warn like the category and tag warnings
• tsc --noEmit passes; the built dist/tools/publishPost.js carries both the warn_slug emit and its parsing
• Title and excerpt are wp_slash()-wrapped, consistent with Slash post content before writing in publish-post #211