fix(docs): redirect monitoring-and-debugging.md to observability.md (#50561)

## What

Adds an explicit redirect from
`/docs/guides/monitoring-and-debugging.md` to
`/docs/guides/observability.md`.

## Why

The catch-all `/docs/guides/monitoring-and-debugging/:match*` rule
handles the bare path and subpages, but the root `.md` URL currently
ends up at `/docs/guides/observability/.md`, which 404s:

| URL | Before |
| --- | --- |
| `/docs/guides/monitoring-and-debugging.md` | 308 →
`/docs/guides/observability/.md` (404) |
| `/docs/guides/monitoring-and-debugging` | 308 →
`/docs/guides/observability/` ✓ |
| `/docs/guides/monitoring-and-debugging/logs.md` | 308 →
`/docs/guides/observability/logs.md` ✓ |

The new rule sits before the catch-all so it matches first, mirroring
the existing `observability/access-data.md` rule.

## Testing

- [ ] On the preview, `/docs/guides/monitoring-and-debugging.md`
redirects to `/docs/guides/observability.md` and returns 200

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Bug Fixes**
- Added a permanent redirect from the legacy monitoring and debugging
guide URL to the observability guide.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

apps/www/lib/redirects.js

@@ -205,6 +205,11 @@ module.exports = [
     source: '/docs/guides/telemetry/:match*',
     destination: '/docs/guides/observability/:match*',
   },
+  {
+    permanent: true,
+    source: '/docs/guides/monitoring-and-debugging.md',
+    destination: '/docs/guides/observability.md',
+  },
   {
     permanent: true,
     source: '/docs/guides/monitoring-and-debugging/resolve-issues',