docs(blog): point dead docs links at their current pages (#48683)

## 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 fix (broken links in blog posts).

## What is the current behavior?

Three links in two published blog posts 404:

| link | post |
| --- | --- |
| `/docs/guides/platform/log-drain#generic-http-endpoints` |
`2024-08-15-log-drains.mdx` |
| `/docs/reference/javascript/storage-from-download` |
`2022-12-13-storage-image-resizing-smart-cdn.mdx` |
| `/docs/reference/dart/storage-from-list` | same post |

The log drains guide is at `log-drains` (plural) now, and the JavaScript
and Dart Storage references were reorganized under `file-buckets-*` ids.

## What is the new behavior?

- `guides/platform/log-drain#generic-http-endpoints` becomes
`guides/platform/log-drains#custom-endpoint`
- `reference/javascript/storage-from-download` becomes
`reference/javascript/file-buckets-download`
- `reference/dart/storage-from-list` becomes
`reference/dart/file-buckets-list`

All three destinations return 200.

On the log drains one, the old `#generic-http-endpoints` heading is gone
too, so I checked what replaced it rather than just fixing the path and
leaving a dead fragment. The `#custom-endpoint` section on that page is
the same thing the blog paragraph is describing: "Logs are delivered as
a JSON array via HTTP POST", with a URL, HTTP version, gzip and headers
configuration. That matches "the HTTP Endpoint drain can be used to send
logs to any destination that supports ingestion via HTTP POST requests"
in the post, so I pointed it there. Happy to change it if you would
rather it went to the page top or somewhere else.

## Additional context

Files:

- `apps/www/_blog/2024-08-15-log-drains.mdx` (1)
- `apps/www/_blog/2022-12-13-storage-image-resizing-smart-cdn.mdx` (2)

Verification: all three old URLs confirmed 404, all three replacements
confirmed 200. For the fragment I fetched the log drains page and
confirmed `#generic-http-endpoints` is not among its heading ids while
`#custom-endpoint` is, then read that section's text to check it is the
right one.

I did not touch `apps/www/app/api-v2/md/content.generated.ts`, which
mirrors blog content, since it is generated and will pick this up on its
next build.

Gates run locally: `test:prettier` passes repo wide and the www vitest
suite passes (6 files, 73 tests). I did not run `pnpm build`, which
cannot complete in my environment because the docs
`build:federated-content` step needs `DOCS_GITHUB_APP_PRIVATE_KEY`.

This came out of checking every absolute `supabase.com/docs` link in
`apps/www` and `apps/docs/content` against the live site. Two related
things I found in the same sweep but deliberately left alone, because
the target is a content decision rather than a rename: a few links into
`elevenlabs/examples` whose examples were removed when that repo
restructured by language, and `redwoodjs/redwoodjs-supabase-quickstart`,
whose repo no longer exists.

Freshman contributor, worked through this with Claude Code's help and
checked each URL and heading id myself.


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

* **Documentation**
* Updated JavaScript and Dart getting-started links to their current
client-library pages.
* Corrected the custom HTTP endpoint documentation link for log drains.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Pamela Chia <pamelachiamayyee@gmail.com>

apps/www/_blog/2022-12-13-storage-image-resizing-smart-cdn.mdx

@@ -214,7 +214,7 @@ A few features to look out for in the future:
 
 - Check out the Docs for [Image Resizing](https://supabase.com/docs/guides/storage/serving/image-transformations).
 - Check out the Docs for the [Storage CDN](https://supabase.com/docs/guides/storage/cdn/fundamentals).
-- Get Started today with the [JavaScript](https://supabase.com/docs/reference/javascript/storage-from-download) and [Dart](https://supabase.com/docs/reference/dart/storage-from-list) client libraries.
+- Get Started today with the [JavaScript](https://supabase.com/docs/reference/javascript/file-buckets-download) and [Dart](https://supabase.com/docs/reference/dart/file-buckets-list) client libraries.
 
 ## More Launch Week 6
 

apps/www/_blog/2024-08-15-log-drains.mdx

@@ -50,7 +50,7 @@ Popular destinations like Datadog are supported out of the box. More detailed se
 
 <Img alt="Datadog Logs drain" src="/images/blog/lw12/day-4/datadog-example.png" />
 
-For the providers that are not natively supported yet, the HTTP Endpoint drain can be used to send logs to any destination that supports ingestion via HTTP POST requests. For example, you can send logs to an Edge Function, filter, or restructure the logs, and then dispatch them to an external provider. In the following example, we perform a simple `console.log` of the received JSON payload. Detailed setup guide is available under the [Edge Functions guide](https://supabase.com/docs/guides/platform/log-drain#generic-http-endpoints).
+For the providers that are not natively supported yet, the HTTP Endpoint drain can be used to send logs to any destination that supports ingestion via HTTP POST requests. For example, you can send logs to an Edge Function, filter, or restructure the logs, and then dispatch them to an external provider. In the following example, we perform a simple `console.log` of the received JSON payload. Detailed setup guide is available under the [Edge Functions guide](https://supabase.com/docs/guides/platform/log-drains#custom-endpoint).
 
 <Img
   alt="HTTP Endpoint drain to Supabase Edge Functions"