Fix the nightly link check: tell a broken runner from a dead link, repair every dead link it found

[shoumikhin]

The nightly link-check / lint-urls job has been red for weeks. There are two separate problems behind that, and this PR fixes both.

Problem 1: the script cannot tell a dead host from a broken runner

scripts/lint_urls.sh gets 000 back from curl when there is no HTTP response at
all. That happens for two very different reasons: the host is dead, or the runner
has no working egress. The script treated both as WARN and moved on.

That is unsafe in both directions:

• A genuinely dead host is silently tolerated. The 000 case is exactly the one we
  most want to catch.
• More importantly it also disables the pull request gate. .github/workflows/lint.yml
  runs this same script in diff mode on every pull request, where the only URLs
  checked are the ones that pull request adds. A new link with a typo in the host
  name gives 000 and passes today. A runner with no egress makes every link WARN
  and the whole job green. Both were reproduced locally.

The fix

On 000, probe one known-good URL, https://api.github.com, which the runner
already depends on:

• probe also returns 000, so this runner has no egress: WARN, as before.
• probe returns anything else, so egress works and the problem is the host: retry
  the URL once with a 60 second timeout, then judge it on that result, which for a
  dead host means FAIL.

One deliberate addition worth calling out: the retry with the longer timeout is
more than the minimum needed to close the hole. It is there because the same URLs
were sampled across six nights of nightly logs and a small number of them, one or
two per night out of about 2100, return 000 once and then answer normally. The
default timeout is 10 seconds. Without the retry, this change would turn those
into hard failures and the nightly would stay red for no good reason.

Also removed: the check-host.net fallback

When the first request failed, the script asked check-host.net whether the URL
was reachable from elsewhere and could then overwrite the verdict. That is
removed. Note this makes the script stricter, not more lenient: on a 404 or a 500
the fallback could turn a FAIL into an OK. Dropping it means a real 404 stays a
404, and it also removes a third-party service from the critical path of a lint
job.

Problem 2: eight actually dead links

With problem 1 fixed the nightly would still be red, because there really are dead
links in the tree. The most recent nightly on main
(31350839957)
reported 7 x FAIL 404 and 1 x FAIL 000. All eight are handled here:

file	link	what happened	fix
setup.py	pybind/cmake_example blob/master/setup.py	that project deleted its setup.py, so a master link cannot work	pin to the last revision that still had it
.ci/docker/common/install_openssl.sh	pytorch/pytorch blob/main/.ci/docker/common/install_openssl.sh	the file moved on main	pin to a revision where it exists
.ci/scripts/test_llava.sh	Wikimedia basketball photo	the photo was renamed on Wikimedia, not deleted	point at the same photo under its current name
docs/source/kernel-library-custom-aten-kernel.md	pytorch.org/cppdocs/library.html#...	page and anchor both gone	current cppdocs library index
test/models/export_program.py	pytorch.org/cppdocs/notes/tensor_indexing.html	gone, and it was only mentioned in a comment	drop the URL, keep the sentence
docs/source/success-stories.md	an App Store listing	app delisted	drop the link, keep the text
README.md	github.com/pytorch/executorch/stargazers	returns 404 to an unauthenticated bot, works fine in a browser	@lint-ignore
backends/arm/scripts/toolchain_utils.sh	musl.cc toolchain tarball	serves fine to developers, has never once answered from a GitHub hosted runner	@lint-ignore

Two more URLs are cleaned up along the way: a truncated Qualcomm SDK URL in
backends/qualcomm/scripts/download_qnn_sdk.py that was never a real link, and a
Qwen issue link in examples/models/llama/runner/generation.py pointing at the
old repository name.

On the Wikimedia one specifically: examples/models/llava/README.md already
embeds the renamed photo and documents the caption the model produces for it,
which matches the EXPECTED_PREFIX the script asserts. So this restores the
original input rather than substituting a different picture. Worth knowing, and
the reason this is low risk: no workflow runs .ci/scripts/test_llava.sh. Both
pull.yml and trunk.yml carry the comment "llava gives segfault so not
covering", so llava is not in CI at all right now.

How this was verified

A whole-tree scan is nightly-only, so a pull request run here would only check the
handful of URLs this PR adds. To get real numbers, _link_check.yml was dispatched
in whole-tree mode against this branch's contents
(31417702080):

	main, nightly	this branch, whole tree
URLs scanned	2148	2147
OK	2116	2116
WARN	24	31
FAIL	8	0

Reconciling the two totals, since they should not match exactly:

• 11 URLs leave the scan: 5 replaced by a working equivalent, 4 deleted outright,
  and 2 now marked @lint-ignore.
• 6 join it: the 5 replacements, plus https://api.github.com, which is now
  written in lint_urls.sh as the probe target and so gets scanned itself.
• That is 2148 minus 5, which is 2143. The remaining 4 are URLs that landed on main
  during the day, in examples/models/muse-glimmer/, and are unrelated to this
  change. All 4 pass.

The 7 extra WARNs are the same thing that produces the existing 24: sites that
return 403 to an automated client. Between the two runs, cppreference.com,
stackoverflow.com and vulkan.org happened to answer 403 instead of 200.
Those are already treated as warnings and are not affected by this PR.

The 000 handling itself was also exercised directly, in a scratch repository:

• no egress at all: WARN 000, exit 0, matching a broken runner.
• egress working, host that does not exist: FAIL 000, exit 1.
• OK 200, WARN 403 and FAIL 404 all still behave as before.
• diff mode still only looks at added lines.

[pytorch-bot]

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