docs: move inspect and advisors into observability (#49503)

<!-- CURSOR_AGENT_PR_BODY_BEGIN -->
## Stack

Draft stack extracted from `docs/monitoring`. Merge bottom-up.
Troubleshooting / debugging-guide rewrite is out of scope.

1. **#49503** move inspect and advisors ← **this PR**
2. #49501 split Studio logs from ClickHouse queries
3. #49500 treat reports as signal dashboards
4. #49502 add Observe the data hub
5. #49506 add agent setup components
6. #49504 add hire-an-agent templates
7. #49505 restructure observability nav and overview

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES

## What kind of change does this PR introduce?

Docs update. First layer in the observability stack.

## What is the current behavior?

Inspect and advisors live under Database (`/guides/database/inspect`,
`/guides/database/database-advisors`). Observability readers have to
leave the monitoring section to find them.

## What is the new behavior?

- Moves inspect into `/guides/monitoring-and-debugging/inspect`
- Adds `/guides/monitoring-and-debugging/advisors` (replaces the
Database Advisors page)
- Adds redirects and updates Studio/docs links so old URLs keep working
- Adds both pages to the existing Monitoring nav so they are
discoverable before the later IA PR

## Additional context

Inspect and advisors pages render as standard MDX. Redirects cover
`/docs/guides/database/inspect`,
`/docs/guides/database/database-advisors`, and
`/docs/guides/database/database-linter`. Debugging-guide content is
unchanged except the inspect URL.

## Self-review

- No leftover `/guides/database/inspect` or
`/guides/database/database-advisors` links in docs guides or Studio
linter/AI surfaces (historical blog posts left as-is)
- Smoke test path updated to
`/docs/guides/monitoring-and-debugging/advisors`
<!-- CURSOR_AGENT_PR_BODY_END -->

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

- **New Features**
- Added a centralized Advisors guide for security and performance
checks.
- Updated database inspection guidance with live Postgres statistics,
cache hit-rate context, and query-analysis resources.

- **Documentation**
- Reorganized Advisors and database inspection content under Monitoring
and Debugging.
- Updated navigation, cross-references, in-product help links, and CLI
documentation links.
- Added permanent redirects from previous documentation URLs to preserve
access.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Saxon Fletcher <SaxonF@users.noreply.github.com>
Co-authored-by: Nik Richers <nik@validmind.ai>

e2e/docs/local-smoke/no-credentials.spec.ts

@@ -25,15 +25,13 @@ test.describe('docs dev runs locally without credentials', () => {
     expect(errors.some((message) => SUPABASE_URL_ERROR.test(message))).toBeFalsy()
   })
 
-  test('database-advisors page renders (full content or graceful fallback, never a crash)', async ({
+  test('advisors page renders (full content or graceful fallback, never a crash)', async ({
     page,
   }) => {
-    const response = await page.goto('/docs/guides/database/database-advisors')
+    const response = await page.goto('/docs/guides/monitoring-and-debugging/advisors')
     expect(response?.ok(), `expected 200, got ${response?.status()}`).toBeTruthy()
 
-    await expect(
-      page.getByRole('heading', { name: 'Performance and Security Advisors' })
-    ).toBeVisible()
+    await expect(page.getByRole('heading', { name: 'Advisors' })).toBeVisible()
   })
 
   test('a troubleshooting article page renders without Supabase credentials', async ({ page }) => {