Add and improve SEO descriptions across 205 pages (#2299)

## Summary

Audited all MDX files for SEO and metadata quality. Fixed description
frontmatter issues across 205 documentation pages:

- **Added missing descriptions** to ~105 main content pages
(integrations, platform, hosting, launch, registry, tracking, and more)
- **Improved short descriptions** (under 50 characters) on ~85 pages
with more detailed, accurate summaries
- **Shortened long descriptions** (over 160 characters) on 15 Weave
integration and tools pages
- **Fixed empty descriptions** on 1 page (infrastructure-alerts)
- **Fixed typo** in add-wandb-to-any-library.mdx (decription to
description)

All descriptions are 50-160 characters, written in plain language, and
accurately summarize page content for SEO and navigation purposes. Only
frontmatter was modified; no page content was changed.

Excluded from scope: auto-generated CLI/SDK reference pages, support FAQ
pages, snippet files, locale pages, and redirect stubs.

Co-authored-by: mintlify[bot] <109931778+mintlify[bot]@users.noreply.github.com>
Co-authored-by: John Mulhausen <john.mulhausen@wandb.com>

Author: mintlify[bot]