fix(qwen): the own-key fallback made the override path checkable

Round 9's best finding is that my own round-8 change falsified a rationale I
wrote in round 5. The pre-flight skips the endpoint-override path because "a
built-in's own variable is never consulted there" — then I gave kimi/qwen an
own-key fallback that consults exactly that variable on exactly that path. So a
keyless override config sailed past the check and failed as a 401, which is the
failure the check exists to replace.

Now that the rule is statable for those two providers, they are checked on both
paths ("own key or GADFLY_API_KEY"), while everything else stays silent on the
override path because its rules still are not.

The missing-key hint on the GADFLY_ENDPOINT_* path named the endpoint variable
— telling a keyless operator to put a credential in a Gitea var, which is not
masked, and contradicting the README warning added one round earlier. It now
always names the provider's own masked secret.

Also: the model argument is trimmed, since Go trims GADFLY_MODEL and padding
would otherwise slip past the claude-code exemption; the test job takes
`permissions: contents: read`, being the one job that executes PR-authored
code; and the ollama-cloud rationale is stated once.

Deliberately not taken, with reasons rather than silence: the credential-scrub
bash could be extracted to a testable script like preflight.sh was — fair, and
a follow-up, since moving it now would be a fresh untested surface at merge
time. `tr -d [:space:]` strips POSIX whitespace where Go strips Unicode, which
differs only for a GADFLY_BASE_URL made entirely of non-ASCII spaces. And the
two provider tests overlap but assert different contracts that should be able
to fail independently.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

.gitea/workflows/build-image.yml

@@ -53,6 +53,10 @@ jobs:
   test:
     runs-on: ubuntu-latest
     timeout-minutes: 15
+    # This job executes repository code (`go test`) on pull_request, so it gets
+    # the narrowest token the platform will give it. Nothing here writes.
+    permissions:
+      contents: read
     steps:
       - uses: actions/checkout@v4
         with: