Triage bot (#1417)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> Adds an issue triage workflow and upgrades the duplicate-detection
workflow to a newer Anthropic model.
> 
> - **CI Workflows**:
>   - **New `triage-issues.yml`**:
> - Runs on new issues; installs `opencode` and labels non-English
(`issue/lang`) and incomplete (`issue/incomplete`) reports, posting
guidance comments.
>   - **`duplicate-issues.yml`**:
> - Updates `opencode` model to `anthropic/claude-sonnet-4-5-20250929`
for duplicate detection.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
11a89c6cfec1691c68837d599b8e3fc6888df09e. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

.github/workflows/duplicate-issues.yml

@@ -37,7 +37,7 @@ jobs:
               "webfetch": "deny"
             }
         run: |
-          opencode run -m anthropic/claude-sonnet-4-20250514 "A new issue has been created:'
+          opencode run -m anthropic/claude-sonnet-4-5-20250929 "A new issue has been created:'
 
           Issue number:
           ${{ github.event.issue.number }}