feat(landing): guide intros, why it matters and key takeaways - #2023

🟢 Confidence 10/10 · safe to merge. Content and per-page markup only: every new anchor, CSS rule and quoted figure matches the guide it sits in, and no runtime code changes.
_{no findings · tests not needed · risk low}

Rewrites the opening of nine landing guides, folding the old definition callout into a new guide-lead intro with a Key takeaways box, plus small additions (log-parsing tools table, Sentry discounts, New Relic cost FAQs). Markup, copy and per-page CSS only, and it checks out.

Reply only with the result JSON as above, and nothing else.

_{a582626 · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}