ci: bypass issue-link gate for trusted contributors (#35720)

Bypass the issue-link requirement for external contributors who have
earned the `trusted-contributor` tier label (>=5 merged PRs). Previously
only PRs with the `internal` label skipped the gate, meaning repeat
contributors still had to link an approved issue on every PR. Also
includes minor template and linting tweaks for contributor experience.

## Changes
- Add `trusted-contributor` bypass to the `check-issue-link` job
condition in `require_issue_link.yml`, with a secondary live-label API
fetch inside the script to cover the race where the `external` labeled
event payload doesn't yet include the tier label
- Add a `bypass-trusted-contributor` job in `require_issue_link.yml`
that removes `missing-issue-link` and reopens the PR when the
`trusted-contributor` label arrives after enforcement has already closed
it
- Reorder steps in `tag-external-contributions.yml` so the tier label is
applied *before* the `external` label — eliminates the race window
entirely since `trusted-contributor` is already on the PR when the
downstream `labeled` event fires
- Switch the tier-label step from `GITHUB_TOKEN` to the app token so the
`trusted-contributor` labeled event propagates to downstream workflows
- Add `hotfix` to allowed PR title types in `pr_lint.yml`
- Promote the English language policy to a blockquote callout in issue
and PR templates; add a "do not begin work without assignment" note to
the feature request template

.github/ISSUE_TEMPLATE/feature-request.yml

@@ -6,7 +6,9 @@ body:
   - type: markdown
     attributes:
       value: |
-        Thank you for taking the time to request a new feature. All contributions must be in English. See our [language policy](https://docs.langchain.com/oss/python/contributing/overview#language-policy).
+        > **All contributions must be in English.** See the [language policy](https://docs.langchain.com/oss/python/contributing/overview#language-policy).
+
+        Thank you for taking the time to request a new feature.
 
         Use this to request NEW FEATURES or ENHANCEMENTS in LangChain. For bug reports, please use the bug report template. For usage questions and general design questions, please use the [LangChain Forum](https://forum.langchain.com/).
 
@@ -18,6 +20,8 @@ body:
         * [LangChain ChatBot](https://chat.langchain.com/)
         * [GitHub search](https://github.com/langchain-ai/langchain),
         * [LangChain Forum](https://forum.langchain.com/),
+
+        **Note:** Do not begin work on a PR unless explicitly assigned to this issue by a maintainer.
   - type: checkboxes
     id: checks
     attributes: