[autofix] reddit/hot: EMPTY_RESULT

## Summary
OpenCLI autofix repaired this adapter locally, and the retry passed.

## Adapter
- Site: `reddit`
- Command: `hot`
- OpenCLI version: `1.8.7`

## Original failure
- Error code: `EMPTY_RESULT`

~~~
opencli reddit hot --limit 3 -> []
~~~

The command exits 0 and returns an empty array. No error is raised, so
`--trace retain-on-failure` produces no artifact at all: the silent empty
result bypasses the entire diagnostic toolchain.

## Root cause
Reddit now returns an empty Listing (`dist: 0`) for the global frontpage JSON
endpoints. Verified by loading each endpoint directly in a browser tab and
reading the payload:

| endpoint | `dist` | result |
|---|---|---|
| `/hot.json` | 0 | empty |
| `/.json` | 0 | empty |
| `/best.json` | 0 | empty |
| `/r/popular/hot.json` | 3 | OK |
| `/r/all/hot.json` | 3 | OK |
| `/r/<sub>/hot.json` | 3 | OK |</sub>

`clis/reddit/hot.js` used `/hot.json` for the frontpage branch, so the
frontpage path silently returned `[]` while the `--subreddit` path kept working.

## Local fix summary

~~~
Frontpage path changed from '/hot.json' to '/r/popular/hot.json', and explicit
guards added: non-ok HTTP, non-Listing payloads, and empty listings now throw
instead of returning [] (the empty case names dist= and points at
--subreddit/popular).
~~~

## Verification
- `opencli reddit hot --limit 3` -> real posts (rank/title/score/comments/media)
- `opencli reddit hot --subreddit LocalLLaMA --limit 2` -> still OK
- `opencli validate reddit` -> PASS (21 commands, 0 errors, 0 warnings)
- `node scripts/check-silent-column-drop.mjs` -> no new violations

_Issue filed by OpenCLI autofix after a verified local repair._

Start in clis/reddit/hot.js and reproduce the empty frontpage result with `opencli reddit hot --limit 3`; compare the frontpage and subreddit branches with the endpoint behavior documented here. Verify that failures and empty listings no longer pass silently, then run `opencli validate reddit` and `node scripts/check-silent-column-drop.mjs`; done means frontpage and subreddit commands return real results without new validation violations.

Written by the indexing model from the issue text.