feat(landing): Sentry pricing guide - #1570

🟡 Confidence 6/10 · needs attention. Held at 6 because a correctness warning is open.
_{1 warning −1 · tests not needed · risk low · 1 defect fixed in earlier rounds}

Adds the /guides/sentry-pricing landing page, its Guides index and llms.txt entries, and the two screenshots it uses. The Sentry content itself is unchanged since the last review; the still-open Loguru snippet import from finding F2 keeps this from being clean.

• New /guides/sentry-pricing Astro page with plans, rates and worked bills
• Guide listed in index.astro and llms.txt.ts
• Both guide-figure screenshots now ship under public/screenshots/guides/

Still open from earlier reviews

• 🟠 Warning · F2 · Snippets import LoggingHandler from a submodule no OTel package ships · apps/landing/src/pages/guides/loguru.astro:229

Production impact

_{8c53d4d · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}